Low-cost high-heat-conduction die-casting magnesium alloy and manufacturing method therefor

Abstract

A die-casting magnesium alloy. The die-casting magnesium alloy comprises, by mass percent, 1% to 5% of La, 0.5% to 3% of Zn, 0.1% to 2% of Ca, 0.1% to 1% of Mn and the balance Mg and other inevitable impurities. The die-casting magnesium alloy manufacturing method comprises smelting, refinement and die-casting. The die-casting magnesium alloy has good mechanical performance, die-casting performance and heat conduction performance.

Claims

1. A heat-conduction die-casting magnesium alloy consisting of by mass, La: 1 to 5%; Zn: 2.5 to 3%; Ca: 0.1 to 2%; Mn: 0.1 to 1%; and the balance is Mg and other inevitable impurities; wherein the magnesium alloy has a microstructure comprising -magnesium matrix and precipitation phases, and wherein the -magnesium matrix comprises fine grains and a small amount of relatively larger grains, and the relatively larger grains have a volume ratio of 20% or less; and wherein the fine grains have a size of 3-15 m and the relatively larger grains have a size of 40-100 m.

2. The heat-conduction die-casting magnesium alloy of claim 1, wherein the precipitation phases comprises a MgZnLaCa quaternary phase that is continuously distributed around grain boundaries and a MgZn phase precipitated inside the grains.

3. The heat-conduction die-casting magnesium alloy of claim 2, wherein the MgZn phase has a width of 1-20 nm and a length of 10-1000 nm.

4. The heat-conduction die-casting magnesium alloy of claim 1, wherein the magnesium alloy has a thermal conductivity of 110 W/m.Math.K or more, a tensile strength of 200-270 MPa, a yield strength of 150-190 MPa, and an elongation of 2-10%.

5. A manufacturing method for a heat-conduction die-casting magnesium alloy, comprising the following steps: (1) melting pure Mg ingots and pure Zn ingots in a smelting furnace; (2) adding MgCa and MgMn master alloys to the smelting furnace and melting them completely; (3) adding MgLa master alloy to the smelting furnace and melting it completely, and adding flux at the same time to cover the surface of a resulting melt; (4) refining the melt; (5) cooling the refined melt to 630-750 C.; and (6) die-casting the melt to obtain a heat-conduction die-casting magnesium alloy consisting of by mass: La: 1 to 5%; Zn: 2.5 to 3%; Ca: 0.1 to 2%; Mn: 0.1 to 1%; and the balance is Mg and other inevitable impurities; wherein the magnesium alloy has a microstructure comprising -magnesium matrix and precipitation phases, and wherein the -magnesium matrix comprises fine grains and a small amount of relatively larger grains, and the relatively larger grains have a volume ratio of 20% or less; and wherein the fine grains have a size of 3-15 m and the relatively larger grains have a size of 40-100 m.

6. The manufacturing method for the heat-conduction die-casting magnesium alloy of claim 5, wherein in the step (1), temperature in the smelting furnace is controlled to 700-760 C., and the melting is performed under the protection of SF.sub.6 gas.

7. The manufacturing method for the heat-conduction die-casting magnesium alloy of claim 5, wherein in the step (2), temperature in the smelting furnace is controlled to 700-760 C., and the melting is performed under the protection of SF.sub.6 gas.

8. The manufacturing method for the heat-conduction die-casting magnesium alloy of claim 5, wherein in the step (3), temperature in the smelting furnace is controlled to 700-760 C., and the smelting is performed under the protection of SF.sub.6 gas.

9. The manufacturing method for the heat-conduction die-casting magnesium alloy of claim 5, wherein in the step (4), temperature in the smelting furnace is controlled to 730-780 C., and Ar gas is introduced into the melt or the melt is manually stirred, while flux is simultaneously added for refining for 5-15 minutes to obtain a refined melt; and then the refined melt is kept standing at 730-760 C. for 80-120 minutes.

10. The manufacturing method for the heat-conduction die-casting magnesium alloy of claim 5, wherein in the step (6), the die-casting is controlled such that an injection speed is 2-50 m/s, a die temperature is 220-400 C., and a casting pressure is 10-90 MPa.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a figure shows the optical microstructure of the low-cost high-heat-conduction die-casting magnesium alloy of Example E.

(2) FIG. 2 is a scanning electron micrograph of the microstructure of the low-cost high-heat-conduction die-casting magnesium alloy of Example E.

(3) FIG. 3 is a transmission electron micrograph of the microstructure of the low-cost high-heat-conduction die-casting magnesium alloy of Example E.

DETAILED DESCRIPTION

(4) The low-cost high-heat-conduction die-casting magnesium alloy of the present invention and the manufacturing method therefor will be further explained with reference to the accompanying drawings and specific Examples, while the technical solutions of the present invention are not limited by the explanations.

EXAMPLES A-E AND COMPARATIVE EXAMPLE F

(5) The above Examples and Comparative Example are obtained by the manufacturing method for the low-cost high-heat-conduction die-casting magnesium alloy of the present invention, including the steps of:

(6) 1) melting pure Mg ingots and pure Zn ingots in a smelting furnace under the protection of SF.sub.6 gas, wherein smelting temperature is controlled to 700-760 C.;

(7) 2) adding MgCa and MgMn master alloys to the smelting furnace and melting completely under the protection of SF.sub.6 gas, wherein smelting temperature is controlled to 700-760 C.;

(8) 3) adding MgLa master alloy to the smelting furnace and melting completely under the protection of SF.sub.6 gas, wherein smelting temperature is controlled to 700-760 C., and adding flux RJ-5 at the same time to cover melt surface;

(9) 4) refining the melt, wherein smelting temperature is controlled to 730-780 C., introducing Ar gas into the melt while adding RJ-5 flux for refining for 5-15 minutes to obtain a refined melt; then standing at 730-760 C. for 80-120 minutes and controlling the mass percentage of chemical elements in the melt to the values as shown in Table 1;

(10) 5) cooling the refined melt to 630-750 C. to obtain a melt for die-casting.

(11) 6) die-casting the melt by a 300-ton cold chamber die casting machine to obtain low-cost high-heat-conduction die-casting magnesium alloys of different sizes, wherein the die-casting parameters are controlled as: the shot speed for injecting the melt for die-casting in step (5) into the die-casting machine is 2-50 m/s, die temperature is 220-400 C., and casting pressure is 10-90 MPa.

(12) Table 1 shows the mass percentages of the chemical elements of magnesium alloys of the above Examples and Comparative Example.

(13) TABLE-US-00001 TABLE 1 (wt %, the balance are Mg and other inevitable impurities) Number La Zn Ca Mn Die-casting size A 5 0.5 2 0.1 150 mm 50 mm 2 mm B 1 3 0.1 0.5 100 mm 40 mm 1 mm C 4 2 1 1 100 mm 40 mm 1 mm D 2 2.5 1 0.5 1000 mm 50 mm 0.6 mm E 5 0.5 0.5 0.9 1200 mm 50 mm 0.6 mm F 5 0.5 0.9 1200 mm 50 mm 0.6 mm

(14) Table 2 shows specific process parameters of the manufacturing method for magnesium alloys of the above Examples and Comparative Example.

(15) TABLE-US-00002 TABLE 2 Step (5) Step (1) Step (2) Step (3) Step (4) temperature Step (6) smelting smelting smelting furnace refining standing standing after shot die casting temperature temperature temperature temperature time temperature time cooling speed temperature pressure Number ( C.) ( C.) ( C.) ( C.) (min) ( C.) (min) ( C.) (m/s) ( C.) (MPa) A 720 740 740 780 5 750 80 630 50 230 12 B 740 760 720 760 10 740 80 650 15 400 80 C 740 760 720 760 10 740 100 750 3 300 50 D 750 750 730 760 15 740 120 700 10 260 20 E 760 760 740 750 15 750 120 720 6 240 10 F 760 760 740 750 15 750 120 720 6 240 10

(16) Magnesium alloy samples of Examples A-E and Comparative Example F were tested. In addition, the ignition point and creep performance tests were also conducted for Example E and Comparative Example F. The test results are shown in Table 3.

(17) Table 3 shows the overall performance parameters of the magnesium alloys of the above Examples and Comparative Example.

(18) TABLE-US-00003 TABLE 3 Thermal Tensile Yield Die casting Ignition conductivity strength strength Elongation surface with or point Steady creep rate Number W/(m .Math. K) (MPa) (MPa) (%) without defects ( C.) at 200 C./60 MPa A 130 260 185 4% without defects B 115 280 195 10% without defects C 120 270 170 2% without defects D 115 275 174 5% without defects E 115 280 170 6% without defects 847 1.4 10.sup.7 s.sup.1 F 110 274 162 7.6% without defects 764 2.5 10.sup.6 s.sup.1

(19) As can be seen from Table 3, all magnesium alloys of Examples A to E of the present invention have a tensile strength of 260 MPa or more, a yield strength of 170 MPa or more and an elongation of 2% or more. Therefore, the magnesium alloys of Examples have comprehensive mechanical properties such as high strength and good tensile elongation property. In addition, thermal conductivities of all the magnesium alloys of Examples A to E of the present invention are 115 W/(m.Math.K) or more, indicating the excellent thermal conductivity of the magnesium alloys of the above Examples.

(20) As can be seen from the combination of Table 1, Table 2 and Table 3, although same manufacturing process parameters were used for Example E and Comparative Example F, the thermal conductivity of Comparative Example F (i.e. 110 W/(m.Math.K)) was lower than that of Example E, the ignition point (the ignition point characterizes the degree of difficulty of oxidation and combustion of the alloy in the smelting process, i.e. the higher ignition point an alloy has, the less likely it is oxidized and combusted during the smelting process, while the lower ignition point an alloy has, the more likely it is oxidized and combusted) of Comparative Example F (i.e. 764 ( C.)) was also lower than that of Example E, while the steady creep rate at 200 C./60 MPa (the steady creep rate characterizes the deformation rate of the alloy when subjected to external loads for a long time at high temperature, i.e. the lower creep rate an alloy has, the less likely the alloy deforms at high temperature and the better the stability of the alloy become, otherwise, the alloy tends to deform at high temperature have a poor stability) of Comparative Example F (i.e. 2.510.sup.6 S.sup.1) was higher than that of Example E, since Comparative Example F did not include Ca. Thus, the above demonstrates that the addition of Ca can effectively improve the ignition point and creep resistance of the alloy.

(21) FIGS. 1, 2 and 3 show the optical micrograph, the scanning electron micrograph and the transmission electron micrograph of the low-cost high-heat-conduction die-casting magnesium alloy of Example E, respectively. It can be seen from FIG. 1 that the -Mg matrix of the low-cost high-heat-conduction die-casting magnesium alloy mostly forms fine grains with grain sizes of 3-15 m, while only a small amount of large crystal grains having sizes of 40-100 m are present. As can be seen from FIG. 2, there are many second phases (precipitate phase) distributed at the grain boundary. These phases can also effectively improve the mechanical properties and creep resistance of the alloy. These phases are distributed in a continuous manner around the grain boundary. The energy spectrum analysis results show that these second phases are MgZnLaCa quaternary phase. As can be seen from FIG. 3, there are also precipitated phases inside the grains, which have a width of 1-20 nm and a length ranging from 10-1000 nm. The energy spectrum analysis shows that these phases are MgZn phase, which reduces the Zn content in the Mg matrix, weakens the effect of alloying elements on the thermal conductivity, and improves the mechanical properties of the alloy.

(22) It should be noted that the above is only specific Examples of the present invention. It is obvious that present invention is not limited to the above Examples, and there are many similar changes. All variations that a person skilled in the art derives or associates directly from the disclosure of the present invention shall fall within the protection scope of the present invention.