ALUMINUM WELDING FILLER METAL, CASTING AND WROUGHT METAL ALLOY

Abstract

A composition for producing aluminum casting, wrought, and welding filler metal alloys having a chemistry comprising Si varying from approximately 0.1 and 0.9 wt %, Mn varying from approximately 0.05 to 1.2 wt %, Mg varying from approximately 2.0 to 7.0 wt %, Cr varying from approximately 0.05 to 0.30 wt %, Zr varying from approximately 0.05 to 0.30 wt %, Ti varying from approximately 0.003 to 0.20 wt %, and B varying from approximately 0.0010 to 0.030 wt %, and a remainder of aluminum and various trace elements. The alloy is particularly suited to producing high strength structures such as automobiles, truck trailers, rail cars, and ships. It is the first 6xxx series weld filler metal that can be post-weld thermally treated and can weld 3xxx, 5xxx, 6xxx, and 7xxx series base alloys yielding far superior mechanical properties than those attainable from any other aluminum filler metal.

Claims

1. A composition for producing aluminum casting, wrought, and filler metal alloys from the same chemistry having a composition comprising silicon in a weight percentage of between approximately 0.01% inclusive and 0.9% inclusive; manganese in a weight percentage of between approximately 0.05% inclusive and 1.2% inclusive; magnesium in a weight percentage of between approximately 2.0% inclusive and 7.0% inclusive; chromium in a weight percentage of between approximately 0.05% inclusive and 0.30% inclusive; zirconium in a weight percentage of between approximately 0.05% inclusive and 0.30% inclusive; titanium in a weight percentage of between approximately 0.003% inclusive and 0.20% inclusive; and boron in a weight percentage of between approximately 0.0010% inclusive and 0.030% inclusive.

2. In accordance with claim 1, a composition comprising silicon in a weight percentage of between approximately 0.50% inclusive and 0.70% inclusive; manganese in a weight percentage of between approximately 0.05% inclusive and 0.20% inclusive; magnesium in a weight percentage of between approximately 5.7% inclusive and 6.1% inclusive; chromium in a weight percentage of between approximately 0.05% inclusive and 0.20% inclusive; zirconium in a weight percentage of between approximately 0.05% inclusive and 0.15% inclusive; titanium in a weight percentage of between approximately 0.003% inclusive and 0.10% inclusive; and boron in a weight percentage of between approximately 0.0010% inclusive and 0.010% inclusive.

3. In accordance with claim 1, a composition comprising silicon in a weight percentage of between approximately 0.30% inclusive and 0.50% inclusive; manganese in a weight percentage of between approximately 0.50% inclusive and 1.0% inclusive; magnesium in a weight percentage of between approximately 3.4% inclusive and 3.7% inclusive; chromium in a weight percentage of between approximately 0.05% inclusive and 0.20% inclusive; zirconium in a weight percentage of between approximately 0.05% inclusive and 0.15% inclusive; titanium in a weight percentage of between approximately 0.003% inclusive and 0.10% inclusive; and boron in a weight percentage of between approximately 0.0010% inclusive and 0.010% inclusive.

4. In accordance with claim 1, a 6xxx series aluminum alloy composition that provides for the use of a single chemistry to produce castings, weld filler metals, and wrought base metal alloys that can be welded together into structures that will have closely matched mechanical and physical properties throughout resulting in welded structures that have mechanical properties substantially higher than anything achievable with the currently available aluminum alloys.

5. In accordance with claim 3, a 6xxx series aluminum alloy filler metal composition that will respond to post-weld thermal treatments thereby allowing the restoration of mechanical properties degraded in the heat affected zone of heat treated alloys during welding operations thus yielding finished weldments where the resulting weld joint yields mechanical properties that meet or exceed that of both cast and wrought aluminum alloy components.

6. In accordance with claim 2, a 6xxx series aluminum filler metal alloy composition capable of welding 3xxx, 5xxx, 6xxx, and 7xxx series aluminum metal alloys yielding higher mechanical properties and fatigue strength than can be achieved with any 4xxx or 5xxx series aluminum filler metal alloys currently available.

7. In accordance with claim 3, a 6xxx series aluminum filler metal alloy composition capable of welding silicon based aluminum casting alloys to wrought 5xxx and 6xxx series aluminum alloys containing less than 3% Mg, yielding significantly higher mechanical properties than can be achieved with the 4xxx or 5xxx series aluminum filler metal alloys currently available.

8. In accordance with claim 3, a 6xxx series aluminum filler metal alloy composition capable of being post-weld aged or post-weld heat treated and aged with mechanical properties in the as-welded or post-weld thermally treated condition that substantially exceed the post-welded properties of all of the currently available 4xxx and 5xxx series aluminum filler metal alloys while maintaining a high level of toughness.

9. In accordance with claim 3, a 6xxx series aluminum filler metal alloy that can be used for elevated temperature applications up to 250 deg. F. with higher mechanical properties than any other suitable filler metal alloy designed for elevated temperature applications that is currently available.

10. In accordance with claim 1, a 6xxx series aluminum filler metal alloy composition that can be adjusted to provide color matching for post-weld anodizing treatments of various welded aluminum alloy components.

11. In accordance with claim 1, a 6xxx series aluminum filler metal alloy composition that can be adjusted to provide corrosion protection properties that match or exceed those of the aluminum alloy components being welded.

12. In accordance with claim 1, a 6xxx series aluminum filler metal alloy composition that will provide a typical electrical conductivity of approximately 23 IACS which will allow this alloy to be arc welded in the globular transfer or short arc mode which is not now possible with any other aluminum filler metal currently available.

13. In accordance with claim 11, a 6xxx series aluminum filler metal alloy composition that creates higher resistance heating of the electrode during arc welding, resulting in reduced thermal energy required in the arc plasma which in turn produces a more stable droplet transfer with reduced Mg burn off and less undesirable condensation of vaporized Mg (referred to as smut) on the base metal surfaces resulting in lower shielding gas requirements and reduced welding costs.

14. In accordance with claim 11, a 6xxx series aluminum filler metal alloy composition that increases melt-off rate of the electrode during arc welding and consequently a reduction of total heat input resulting in a reduction of the loss of mechanical properties in the heat affected zone and less mechanical distortion of aluminum base metal components being welded.

15. In accordance with claim 11, a 6xxx series aluminum filler metal alloy composition that increases melt-off rate of the electrode during arc welding resulting in higher welding speeds and lower electrode consumption which reduces welding costs.

16. In accordance with claim 6, a 6xxx series aluminum filler metal alloy composition that because of increased tensile strength, shear strength, and fracture toughness, provides the opportunity to reduce weld bead size and increase welding speeds resulting in cost savings in welding operations.

17. In accordance with claim 1, a 6xxx series aluminum welding filler metal alloy composition that has lower molten surface tension than any 5xxx series filler metal alloy thus producing lower and flatter weld beads thereby improving the fatigue strength of the welded joint.

18. In accordance with claim 1, a 6xxx series aluminum filler metal alloy that has higher molten fluidity than any current 5xxx series filler metal alloy thus increasing wettability during welding which improves fusion and flattens the edge of the weld bead thereby improving fatigue strength of the welded joint.

19. In accordance with claim 1, a 6xxx series aluminum welding filler metal alloy that has a lower liquid solubility for hydrogen than any 5xxx series filler metal alloy, thus reducing the volume of hydrogen porosity present in solidified welded joints.

20. In accordance with claim 1, a 6xxx series wrought aluminum alloy for use in producing forged and cold headed products such as rivets, and similar products which can be cold formed, then solution heat treated, quenched and aged to yield substantially higher mechanical properties along with the desired physical properties of corrosion resistance and anodized color matching.

Description

BRIEF SUMMARY OF THE DRAWINGS

[0028] The description herein makes reference to the accompanying drawings wherein like reference numerals refer to like parts throughout the several views and wherein:

[0029] Some of the metallurgical and mechanical aspects of this invention are best illustrated through the use of graphical representations of the principals involved. Several graphs and charts have been included to illustrate the critical elements of this invention.

[0030] FIG. 1 is a table showing the chemical composition of the invention alloy along with alloys 1 & 2 which are two preferred embodiments.

[0031] FIG. 2 is a graph showing the tensile strength of various 5xxx series filler metal alloys as it varies with increasing percentages of the alloying elements Mg and Mn in combination. Included on this graph is a band of prophetic properties that are achievable with the invention alloy composition depending on the chemical compositions chosen within the allowable limits and the properties that are achievable as-welded or in various states of thermal treatment.

[0032] FIG. 3 is a graph showing the tensile strength of various 4xxx series alloy filler metals as it varies with increasing percentages of its alloying elements.

[0033] FIG. 4 is a graph showing the typical tensile strength of as-welded 5554 along with a range of prophetic tensile strengths that the invention alloy 2 is capable of producing as welded and when post-weld thermally treated.

[0034] FIG. 5 is a graph showing the Electrical Conductivity of various aluminum alloys as it is affected by the percentage of alloying elements Si and Mg.

[0035] FIG. 6 is a table showing the typical tensile strength of two aluminum alloys 6063 and 6061 as the content of Mg2Si is increased. The effects of increasing Mg2Si on the mechanical properties of a weldment are illustrated.

[0036] FIG. 7 is a chart showing weldment cooling rates for varying welding heat inputs. The critical cooling range for aluminum is illustrated.

[0037] FIG. 8 is a table showing the typical solid-solution strengthening provided by the increasing combination of Mg plus Mn when alloyed into a relatively pure aluminum matrix without Si present. It also shows the impact of including homogenous Mg2Si into pure aluminum along with free Mg and Mn. The chart shows the typical shear, tensile, and yield strengths of various aluminum filler metal alloys including the prophetic properties of the invention alloys.

[0038] FIG. 9 is a chart showing the electronegative potential of various solid solutes or constituents in aluminum alloys.

[0039] FIG. 10 is a chart showing the as-welded fatigue strength of various aluminum alloys.

[0040] FIG. 11 is a chart showing the toughness of various aluminum alloys welded with various popular aluminum weld filler metal alloys.

[0041] FIG. 12 is a drawing showing a typical fillet weld and butt weld joint.

[0042] FIG. 13 is a chart showing the effect of increasing alloy content on the fluidity of aluminum alloys.

[0043] FIG. 14 is a chart showing the effect of increasing alloy content on the surface tension of aluminum alloys.

DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENT

[0044] Historically, welding filler metal alloys for aluminum have been developed by simply adapting the chemistries of already existing brazing alloys or by slightly modifying the chemistries of the cast or wrought alloys to be welded. In the case of the 4xxx series of welding alloys, most were adaptations of pre-existing brazing alloys. In the case of the filler metal alloys for welding cast alloys, they are simply a replication of the chemistry of the cast alloys to be welded with some modifications for elements that will burn off during welding. In the case of the 5xxx series filler metal alloys, they also are a slightly modified chemistry of the 5xxx series wrought alloys to be welded. Consequently, welding engineers struggle to produce welds where the strength of the weld joint significantly exceeds the strength of the base metals being welded. Because of the mechanical defects that are inherently present in all weld joints, it is critical for dynamically and in some cases statically loaded structures to have the strength of the weld joints exceed the strength of the base metals being joined. This becomes particularly critical in fillet welds and in partially penetrated butt-joint welds (See FIG. 12 for pictures of a typical fillet and butt weld joint). It is estimated that in general manufacturing operations, approximately 70% of all welds end up with partial penetration. In these cases, the weld metal bears all of the stress loads when in service. It becomes critical that weld joints have superior strength and toughness if welded structures are to meet their designed service life. This invention addresses this limitation of the currently available families of aluminum welding filler metal alloys.

[0045] Heat generated during the welding process has always been a negative. Heat deteriorates the properties of the base metal in the heat affected zone. Until now, there have not been any alloys registered with the Aluminum Association for welding or listed in the AWS A5.10 filler metal specification for aluminum that have been specifically designed to optimize their mechanical and physical properties by utilizing the thermal processes that are present in GMA and GTA welding operations. Additionally, when attempts have been made to produce higher strength 5xxx series welding filler metals they have been limited because, as the strength of the alloys was increased through maximizing Mg and Mn additions, the alloys very rapidly reached the point where the ductility of the alloy was lowered such that they could no longer be fabricated into welding wire or rods. The chemistry of the 6xxx series welding filler metal alloy of this invention was designed so that it could be thermally processed in such a way as to allow the alloy to be drawn into welding wire of the popular sizes. Next, the chemistry was designed so as to achieve maximum potential mechanical properties during the melting, rapid solidification, and subsequent cooling to room temperature of the weld joint. In addition to this, the invention alloy composition was designed to be adjustable so as to be able to adjust the corrosion properties and to be able to match the anodizing characteristics of the base metal alloys being welded. It was also a design objective to be able to adjust the Mg content in the alloy so that it could be used to weld 5454 and other base alloys that are used in elevated temperature applications up to 250 degrees F. Finally, this new 6xxx series filler metal alloy can be used to weld the 6xxx series wrought alloys and be responsive to thermal treatments such that after post-weld thermal treatment operations, the strength of the filler metal exceeded that of the 6xxx series base metals being welded without a loss of toughness.

[0046] Aluminum alloys are divided into two categories, heat treatable and non-heat treatable. The 6xxx series alloys are heat treatable. The principal strengthening mechanism in these alloys is achieved through dissolving Si and Mg into solution through a solution heat treatment operation, then quenching to lock them in solution at room temperature. The alloy is then artificially aged at elevated temperatures to precipitate out Mg2Si as coherent homogeneously dispersed particles that stress and thereby strengthen the microstructure. Non-heat treatable alloys such as the 3xxx, 4xxx and 5xxx series alloys achieve their mechanical properties through solid solution strengthening of the dissolved alloying elements, primarily Mn in the case of 3xxx series alloys, Si in the case of the 4xxx series alloys and Mg plus Mn in the case of the 5xxx series alloys. These alloys achieve additional strength through cold working operations. However, in the as-welded condition the 3xxx, 4xxx, and 5xxx series filler metals obtain their strength solely by solid solution strengthening of their principal alloying elements since no cold working is done after welding.

[0047] In the invention alloy composition, Mn is used in very limited amounts, when in the presence of higher magnesium contents, since it quickly creates a microstructure that results in brittle fracture when the extreme levels of cold work required to fabricate wire is encountered. Cu content is closely controlled in the base metal composition to reduce quench sensitivity during welding.

[0048] The 4xxx series welding filler metals cannot be used to weld the high strength 5xxx series base metal alloys and they have limited use for welding the high strength 6xxx series base metals due to their high Si content and low toughness properties.

[0049] The currently available 5xxx series weld filler metal alloys contain Mg and Mn as the principal alloying elements and contain no intentional additions of Si. FIG. 3 shows the effect of increasing additions of Mg and Mn. on the tensile strengths of the 5xxx series welding filler metal alloys. In the as-welded condition, they rely solely on the solid solution strengthening provided by Mg and Mn. No free silicon is present in the microstructure. FIG. 8 shows the effect of adding Si to form Mg2Si in combination with Mg and Mn resulting in increased tensile and shear strengths.

[0050] In the 6xxx series of wrought alloys, the alloying elements of Si and Mg are carefully formulated to produce Mg2Si in the final microstructure with little or no excess Si or Mg present after the final fabrication and heat treatment operations are completed.

[0051] The strengthening mechanism of the combination of Mg2Si with the addition of excess Mg at varying levels in the invention alloy composition was chosen to achieve the desired properties in the welding filler metal of this invention. The maximum solid solubility of Mg2Si in aluminum is 1.85%. In the 6xxx series alloys varying amounts of Mg2Si are used to achieve their mechanical properties (See FIG. 6). For this invention, various levels of Mg2Si have also been chosen to achieve the desired as-welded properties after welding the 5xxx series alloys and to achieve the desired as-welded and post-weld thermal treated properties desired when welding the 6xxx series alloys. The presence of Mg2Si that exceeds the solubility limit of 1.85% manifests itself in the as-welded microstructure as large particles of heterogeneous Mg2Si that do not respond to thermal treatments and have the other undesirable attribute of tying up excess Mg and not allowing it to be available for solid solution strengthening of the matrix. It is also known that Mg present in solid solution lowers the solubility of Mg2Si from the 1.85% level in pure aluminum. Therefore, the range of levels of Mg2Si in the new filler metal alloy composition was conservatively chosen in order to avoid producing excess Mg2Si that would be out of solution in the as-welded or post-weld thermally treated microstructures.

[0052] In the invention alloy composition, the limits of Si content are set at approximately 0.1% to 0.9% by weight, the limits of Mn content are set at approximately 0.05% to 1.2% by weight and the limits of Mg content in the invention alloy are set at approximately 2.0% to 7.0% by weight. For each alloy formulated within the limits of the invention alloy composition, the Mg2Si content is set at approximately 1.1% to 1.5% by weight. These levels avoid the problems of producing excess Mg2Si when significant levels of excess Mg are present. The ratio by weight of Mg to Si in Mg2Si is 1.73 to 1 and this ratio is used to calculate the proper alloy addition levels of Mg and Si. There are a number of other considerations that are designed into the invention alloy composition. Among them is that free Mg must be controlled below 5.2% by weight in order to stay out of corrosion problems that occur when free Mg content gets above that level. The invention alloy composition uses the formation of Mg2Si to remove Mg from solution thereby controlling the free Mg in solution in the alloy to the proper limit of less than 5.2% by weight. This is important for the weld filler metal alloy and the casting alloy.

[0053] The invention alloy composition was designed specifically to take advantage of the thermal processes present during welding operations. In both GMA and GTA welding processes, the filler metal is melted and solidified very rapidly with the time frame being generally less than two seconds and most commonly less than 1 second. See (FIG. 7). This invention was designed to utilize the rapid liquid-to-solid cooling rate of the welding process which is often as much as one hundred times faster than that of casting operations. This rapid solidification rate allows a maximum quantity of combined Mg2Si and free Mg to be put into this alloy and achieve maximum mechanical properties without fear of coarse Mg2Si particles precipitating during solidification.

[0054] The cooling rate that an aluminum alloy experiences after solidification down to room temperature is also critical for an alloy containing Mg2Si and excess Mg. Quench sensitivity is a term commonly used to describe the propensity for an aluminum alloy to precipitate alloy constituents such as Mg2Si as coarse particles in the metal matrix as the alloy cools. The metallurgy of the invention alloy composition was designed so as to create a quench sensitivity that was in concert with the cooling rates experienced in the welding process. Cu, Zn, and Fe increase the quench sensitivity of aluminum alloys and have been controlled to low levels in the invention alloys. The chemistry was further controlled to optimize the effects of thermal energy that is introduced by multiple welding passes. Fe in particular forms negative phases with any solidification and post solidification cooling rate and can only be controlled by chemistry restrictions. Therefore, the invention alloy composition has Fe content controlled below most filler metal alloy specifications.

[0055] For wrought 6xxx series alloys, the critical cooling rates to achieve full design strength specifications are known. For instance, the critical cooling rate to overcome the quench sensitivity of the alloy after solidification, that is the range from 850 to 400 degrees F., depends on the amount of Mg2Si present in the alloy. For an Mg2Si content of 0.8 to 1.1% by weight, the critical cooling rate is 100 degrees F. per minute. For an Mg2Si content of 1.4 to 1.6% by weight, the critical cooling rate increases to 1200 degrees F. per minute. If this cooling rate is not met, Mg2Si will precipitate into the structure as a relatively coarse phase and the mechanical properties of the alloy will be reduced. Therefore, the invention alloy is carefully designed to contain only 1.1 to 1.5% by weight of Mg2Si so as to meet the cooling rates experienced during welding operations as shown in FIG. 7. Again, because the invention alloy composition was designed to contain a maximum amount of free Mg without exceeding the limits required to control corrosion resistance, and knowing that the solubility of Mg2Si is decreased by the presence of free Mg, the control range for Mg2Si is tightly controlled. Even though the chemistry of the invention alloy composition is carefully controlled, due to the variability of the welding process and subsequent thermal treatment operations, the theoretical maximum mechanical properties may not be met in this alloy. Therefore, in FIG. 2, the tensile strength of the 5xxx series of welding filler metal alloys is compared to the prophetic tensile strengths of Alloy 1 of the invention that are shown as a band of possible post-weld tensile strengths achievable under most welding conditions. What we do know is that the invention alloy will provide mechanical properties far above what is now available. Likewise in FIG. 4 the tensile strength of 5554 filler metal is compared to the prophetic tensile strengths of Alloy 2 of the invention that are shown as a band of possible post-weld tensile strengths achievable under most welding conditions and various levels of post-weld thermal treatments.

[0056] The chemistry of the new alloy contains maximum levels of Mg for another specific reason. The melt-off rate of aluminum electrode is based on the welding parameters set into the welding equipment, the shielding gas, the mechanical stick out of the contact tip and electrode, and the physical properties of the electrode including the electrical resistivity of the metal in the electrode. Higher electrical resistivity provides increased heating of the wire as electricity is conducted through it. Higher resistivity of the electrode increases the melt-off rate. Further, aluminum is rarely used in the short-arc transfer welding mode. The resistivity is too low to provide a satisfactory burn-off rate during the short-arc portion of the metal transfer process. An objective of this invention is to increase the melt-off rate of the invention alloy composition in all metal transfer modes including globular, spray and short-arc transfer. FIG. 5 shows the effect of alloying elements on conductivity. Resistivity is the reciprocal of conductivity. Consequently, conductivity changes with to the addition of alloying elements to aluminum and correlates directly to the electrical resistivity of the resulting alloy. Pure aluminum such as alloy 1350 has a conductivity of 62% IACS (international annealed copper standard). For reference purposes, copper has a conductivity rating of 100% IACS and Iron is down at 18% IACS. A 1.5% Mg2Si alloy has a 49% IACS, a 3% Mg alloy a 40% IACS, and a 5% Mg alloy a 29% IACS value. If a typical 1.4% Mg2Si alloy with an electrical conductivity of 50% IACS has 5% Mg added to it, the resultant conductivity of the new alloy can be estimated. In FIG. 5 we show a prophetic value of between 20% and 25% or a typical value of 23% IACS for the invention alloy composition. A 6 point reduction in conductivity from 29 to 23 represents a 21% relative reduction in conductivity from a straight 5% Mg alloy or conversely, a 21% increase in resistivity. The invention alloy composition is approaching the conductivity of iron which is 18% IACS. Iron has well documented melt-off rates and welding characteristics. Short-arc transfer is commonly used in welding steel, taking advantage of its high electrical resistivity. Specifically designed into this alloy is a conductivity that will facilitate short-arc and globular mode transfer. It should be noted that increased melt-off rate is a desired and intended result of this invention. In all metal transfer modes, including spray transfer, increased melt-off rates facilitate welding with a decreased requirement for heat input from the welding equipment thereby reducing the negative effects of reduced mechanical properties in the heat affected zone. Less structural distortion is produced with less heat input as well. Further, electrodes with higher burn off rates can be welded at higher transfer rates increasing welding speeds and thereby reducing welding costs. By increasing the melting rate of the invention alloy composition through increased resistance heating, the thermal energy needed in the arc plasma has been reduced thereby reducing the amount of Mg burn-off in the welding arc. Reduced heat input from the plasma due to increased resistance heating, allows for a more stable droplet transfer in the spray transfer mode, with less metal vaporization. The invention alloy composition reduces the amount or Mg vapors in the arc plasma and the undesirable condensation of these vapors alongside the weld in the form of vapor condensate, known as smut. It is believed that Mg vapors in the arc plasma affects the ionization potential of the shielding gas which gives a different arc characteristic to high Mg filler alloys as compared to other alloy series such as the silicon series filler metal alloys. Therefore, it is anticipated that the invention alloy will allow the use of reduced levels of shielding gas necessary to achieve quality welds.

[0057] The invention alloy composition was also developed to control its corrosion characteristics. The base metal alloys to be welded with this filler metal are used for automotive, truck trailer, rail car and ship building applications to name just a few. These structures spend their lives in harsh environmental atmospheres including the very corrosive effects of sea water. The corrosion characteristics of aluminum filler materials are carefully controlled to insure suitability in a variety of service environments. The new alloys 1 and 2 are specifically designed to have controlled and excellent corrosion resistance as welded.

[0058] FIG. 9 is a table showing the electro negativity of various aluminum alloy compositions. It shows two compositions, that of Al+1% Mg2Si and Al+5% Mg. They both have an electro negative potential very close to that of pure aluminum. Therefore, we believe that the chemical content we have designed into the invention alloy composition will have excellent as-welded corrosion performance. In particular, alloys 1 and 2 will have excellent salt water corrosion performance when welding the typical ship building sheet and plate alloys, 5052, 5086, 5083, 6061, 6082 and 6351.

[0059] FIG. 8 is a table showing the typical as-welded shear and tensile strengths of various aluminum welding filler metal alloys along with the prophetic shear and tensile properties that the invention alloys have. In industry, the number of partially penetrated fillet type welds far exceeds fully penetrated butt type welds. Shear strength is the primary factor considered in designing weld strengths for all partially penetrated welds. Fillet welds represent 70 percent of all structural welds. The invention alloy composition will provide significant increases in tensile, shear and fatigue strengths when compared to all of the other weld filler metal alloys in use today.

[0060] The invention alloy composition was also carefully engineered to weld the 6xxx series base metal alloys. Currently these alloys are welded with 4xxx or 5xxx series alloys that do not respond to post-weld heat treatment and frequently yield lower mechanical properties in the weld joint than are achieved in the base metal with post-weld heat treatment. One of only two exceptions to this is filler metal 4643 which will respond to post-weld heat treatment but has not been a commercially successful alloy for a number of reasons that limit its use. Alloy 4943 is the other exception and it does respond to post-weld treatment giving significantly improved mechanical properties and has its place where high fluidity, increased ease of welding, and low levels of smut deposit are desired. The invention alloy 2 will weld all of the 6xxx series alloys as well as 5454 and will provide excellent elevated temperature service up to 250 degrees F. It fully responds to post-weld thermal treatment processes and will provide higher mechanical properties, higher toughness and reduced crack propagation sensitivity than all of the Si based welding filler metal alloys (See FIG. 12). Alloy 1 will weld all of the 6xxx and 5xxx series base alloys except if elevated temperature service is desired. Alloy 1 will provide large as-welded increases in tensile, shear, and fatigue strengths compared to all other filler metals now available. Alloy 1 will exceed the as-welded strength of all of the current 5xxx series base metal alloys available.

[0061] Experience with aluminum welded structures in service has shown that 90% of all failures are the result of cyclic loading and the failure of weld joints from fatigue. Because there are higher levels of discontinuities in weld joints than in the parent base material, there are higher levels of stress risers in the weld joints. The majority of welds are partially penetrated joints such as fillet welds. In these joints, the weld root in every weld is in fact a sharp notch. This notch acts as a stress riser during cyclic loading. In a fillet weld, the weld bead carries the full stress of cyclic loading. Consequently, the fatigue strength of the weld bead filler metal alloy is of prime importance. The fatigue strength of an aluminum alloy is directly proportional to its tensile strength. The tensile properties of the invention alloy composition are higher than that of any currently available aluminum welding filler metal alloy and consequently the fatigue properties are also higher. The prophetic fatigue strength targeted for the invention alloy composition is illustrated in FIG. 10.

[0062] FIG. 11 shows the documented effect of post-weld aging or post-weld heat treatment and aging on the toughness properties of alloy 6061 welded with 4043, 4643, & 4943. To date, there are no aluminum weld filler metal alloys that will respond to post-weld thermal treatments that do not significantly reduce the energy required to propagate a crack or significantly reduce the crack sensitivity to notches. Consequently, when toughness is a design requirement, 6xxx series base metal welded structures which require post-weld thermal treatments to restore pre-welded properties cannot be used when welded with 4xxx series filler metals. The physical structure of welds is controlled by Specification AWS D1.2 including the amount of allowable discontinuities that are permissible in the weld joint. However, for the majority of welds, over 70% of all welds made in structures are partially penetrated joints. When weld joints are partially penetrated, there is a sharp notch at the root of the weld. Sharp notches significantly reduce the toughness of weld joints. The elimination of the significant loss of toughness in post-weld thermally treated 6xxx alloys is a specific objective of invention alloy 2. Alloy 2 can be post-weld aged or post-weld heat treated and aged without loss of toughness. Alloy 2 also increases fatigue life when stress risers are present. FIG. 11 shows the prophetic toughness for alloy 2. Alloy 2, both as welded and post-weld thermally treated, and alloy 1 as welded are both expected to be similar in toughness to the as-welded properties of 6061 with filler alloy 5356. Both alloy 1 and 2 in the as-welded or post-weld thermally treated condition have much higher toughness than the 4xxx series filler metal alloys. Alloy 2 will allow for the full restoration of the strength properties of 6xxx alloys in the heat affected zone after welding, by post-weld thermal treatments with the retention of high toughness in the welds. The toughness of alloy 1 and 2 are retained while the higher ultimate tensile strengths achieved are significantly higher than currently available filler metal alloys. In FIG. 11 it can be seen that alloy 5183 has higher tensile strength than 5356 but lower toughness. This is due to the brittle effect of increasing the Mn to Mg percentage ratio in these Mg/Mn alloys. Replacing the Mg content with Mn in any Mg/Mn alloy reduces the toughness due to the effects of the Mn. Alloy 1 is designed to replace alloys 5183, 5556 and 5087 while having a lower controlled Mn content. The Mn content in alloy 1 is controlled similarly to alloy 5356. With the addition of higher levels of Mg & Si to convert alloy 1 into a 6xxx series alloy, the resultant toughness is expected to be equal to 5183, 5556 and 5087. Alloy 1 will have no loss of toughness while having significantly higher tensile and shear strengths as compared to the alloys being replaced. This toughness design feature cannot be accomplished with the use of any of the currently available filler metal alloys.

[0063] The invention alloy has also been designed to provide an increase in fluidity and a reduction in surface tension of the molten weld bead when used as a welding filler metal. The chart in FIG. 13 shows the effect of increasing alloy content on the fluidity of molten aluminum alloys. Fluidity of the molten weld bead affects the molten filler metal's wetting action during welding and the weld bead profile after solidification. The chart in FIG. 14 shows the effect of increasing alloy content on the surface tension of molten aluminum alloys. The surface tension on the molten weld bead also affects the weld bead profile after solidification. Higher fluidity and lower surface tension of a molten metal weld bead produces a lower and flatter weld bead profile after solidification. Welding standards control the allowable contour of weld beads. The invention alloy's chemical composition will provide improved wetting action and lower surface tension thereby improving the control over weld bead contour. A weld joint with reduced bead height and a lower angle of incidence of weld metal to base material will have superior fatigue life. The invention alloys will have improved fatigue strength characteristics not only from a material stand point but also from the result of improved physical control over the weld bead contour. This is a specific objective of this invention.

[0064] The invention alloy composition has been designed to reduce hydrogen solubility in molten aluminum weld beads. Increasing alloy content reduces the liquid solubility of hydrogen in aluminum alloys. Silicon reduces the solubility of hydrogen in aluminum to one half that of pure aluminum at the eutectic composition level. Welding specifications limit the amount of allowable hydrogen porosity in welds in order to control mechanical properties. The invention alloys contain substantially greater amounts of alloying elements that the weld filler metal alloys they are intended to replace. Consequently, they will have a lower propensity for hydrogen porosity contamination after welding. This is a specific design objective of this invention.

[0065] Alloys of the invention alloy composition have the ability to be fabricated into wire. In embodiments where the alloys are formed into wire, such wire (i.e. welding filler metal) may be produced on spools for use in GMA welding or it may be cut into straight lengths for GTA welding. These are the two most common forms of aluminum filler metals, but they are not limited to these forms. Typically the linear wire or cut-to-length wire has a diameter of at least 0.010 inches and typically less than 0.30 inches in diameter. In preferred embodiments the wires have one or more diameters, such as 0.023 inches, 0.030 inches, 0.035 inches, 0.040 inches, 0.047 inches, 0.062 inches, 0.094 inches, 0.125 inches, 0.156 inches 0.187 inches, and 0.250 inches. The invention alloys are specifically designed to be able to be drawn into all of the required wire sizes while the Mg2Si matrix phase has been deliberately removed from solid solution through annealing. When the excess Mg is limited to approximately 5.2%, Mn limited to approximately 0.20%, and the Mg2Si phase has been removed from solid solution, the resulting alloy has excellent mechanical cold-working properties.

[0066] The invention alloy composition is designed for use in the production of aluminum castings. The casting chemistries that are available for use in building complex structures such as automobiles, rail cars, truck trailers and many other products require that different weld filler metal alloys be used to weld the structural components together. Because of the large differences between the casting alloys and wrought alloy chemistries being welded together into a single assembly, many compromises have to be made when selecting the appropriate weld filler metal alloys to accomplish the job. The different filler metal alloys that must be used to weld castings to each other and to wrought alloy components prevents designers from being able to achieve structures with the high mechanical properties or desirable physical properties they would like to achieve. From a manufacturing consideration, the use of several different filler metals on a single welded structure requires that separate welding operations be performed. If a single weld filler metal can be used to produce an entire structural component, the weldment can be produced in a single robotic welding cell with one filler metal. This yields a large cost savings in today's automated manufacturing operations.

[0067] There are currently no heat treatable 5xxx series casting alloys. This invention, for the first time, creates an alloy for producing castings that is exactly matched to a weld filler metal alloy where they both make use of Mg2Si and excess Mg to achieve very high as-welded or post-weld thermally treated mechanical properties. The invention alloy composition provides a casting/filler metal alloy combination that can be used to weld castings to 3xxx, 5xxx, 6xxx, and 7xxx series wrought alloys and, for the first time, match the mechanical properties of the three components, both in the as-welded or the post-weld thermally treated condition depending on which chemistry is chosen. For instance, if alloy 1 is chosen, the casting/filler metal pair will yield mechanical strengths in excess of wrought 3xxx and 5xxx series base alloys being welded. If alloy 2 is chosen, the casting/filler metal pair will be suitable for welding 5454 or other base metal alloys intended for high temperature service up to 250 degrees F. This pair can also be used to weld the 6xxx series wrought alloys and will respond to post-weld thermal treatments yielding mechanical properties in excess of the 6xxx series base metal alloys being welded. The invention alloy composition can be used for the production of aluminum structures with mechanical properties that are significantly higher than those possible with currently available casting and welding filler metal alloy combinations. The invention alloy composition casting alloy combined with its matching welding filler metal alloy yields excellent corrosion resistance properties and allows for a good match of corrosion properties between the casting, filler metal, and wrought alloy base metal. The invention alloy composition to be used in various casting/filler metal pairs will yield toughness far beyond that of currently used casting/filler metal combinations. In short, the invention alloy composition allows for the design of welded structures, which combine cast and wrought components with significantly higher strengths and lower fabrication costs.

[0068] It is also anticipated that the invention alloy composition may be used to produce sheet and plate and the many components that can be shaped by roll forming, hydro forming and other shaping processes. By use of the unique combination of Mg2Si and excess Mg, the invention alloy composition lends itself to high degrees of mechanical deformation in the annealed state. The invention alloy composition has been designed to undergo a high degree of cold work without fracturing. Therefore, in the annealed state this alloy can be drawn into wire, or rolled into sheet and plate and subsequently roll formed, pressed or otherwise formed into myriads of shapes for the construction of welded structures. A principal attribute of this alloy composition is that a single chemistry can be used to produce castings, weld filler metals, and wrought base metal alloys that can be welded together into structures that will have closely matched mechanical and physical properties throughout. Structures can be manufactured that have mechanical properties substantially higher than anything achievable with the present alloys available.

[0069] While only certain features of the invention have been illustrated and described herein, many modifications and changes, including numerous alloy compositions will occur to those skilled in the art. It is therefore to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.