A CASTING MAGNESIUM ALLOY FOR PROVIDING IMPROVED THERMAL CONDUCTIVITY

Abstract

A casting magnesium alloy for providing improved thermal conductivity A magnesium alloy for providing improved thermal conductivity includes from 1 wt.% to 5 wt.% of lanthanum, from 1 wt.% to 5 wt.% of cerium or a combination thereof, and from 0.5 wt.% to 3 wt.% of neodymium, from 0.5 wt.% to 3 wt.% of gadolinium or a combination thereof, and from 0.0 wt.% to 0.2 wt.% of yttrium, and up to 0.8 wt.% of praseodymium, and up to 0.8 wt.% manganese, and up to 1.0 wt.% aluminium, and up to 0.8 wt.% zinc, and up to 20ppm beryllium, and with balanced magnesium and inevitable impurities.

Claims

1. A magnesium alloy including: a. from 1 wt.% to 5 wt.% of lanthanum, from 1 wt.% to 5 wt.% of cerium or a combination thereof, and b. from 0.5 wt.% to 3 wt.% of Neodymium, from 0.5 wt.% to 3 wt.% of Gadolinium or a combination thereof, and c. up to 0.2 wt.% of Yttrium, and d. up to 0.8 wt.% of Praseodymium, and e. up to 0.8 wt.% Manganese, and f. up to 1.0 wt.% Aluminium, and g. up to 0.8 wt.% Zinc, and h. up to 20ppm beryllium, and i. with the balance being magnesium and inevitable impurities.

2. A magnesium alloy as claimed in claim 1 including: La 1.0-5.0 wt.%, Ce 1.0-5.0 wt.%, Nd 0.5-2wt.%, Gd 0.5-1.5wt.%, Y up to 0.2wt.%, Pr up to 0.6wt.%, Mn 0.1-0.4 wt.%, and Al up to 0.8wt.%, Zn up to 0.8wt.%, with Be 20ppm with the balance being magnesium and inevitable impurities.

3. A magnesium alloy for providing improved thermal conductivity as claimed in claim 1 or 2 including: La 1.0-3.0 wt.%, Ce 1.0-3.0 wt.%, Nd 0.5-1.5wt.%, Gd 0.5-1.5wt.%, Y up to 0.15wt.%, Pr up to 0.5wt.%, Mn 0.1-0.3 wt.%, and Al up to 0.6wt.%, Zn up to 0.5wt.%, with Be 20ppm with the balance being magnesium and inevitable impurities.

Description

[0058] FIG. 1 is a graph showing the thermal conductivity as a function of temperature for an alloy in accordance with the invention;

[0059] FIG. 2 is a series of photographs of samples of prior art alloys and an alloy in accordance with the invention illustrating high pressure die casting capability; and

[0060] FIG. 3 is a graph showing the strain as a function of time for a prior art alloy and an alloy in accordance with the invention.

[0061] EXAMPLE 1

[0062] Pure magnesium ingots, Mg-5wt.%Mn master alloys and a master alloy containing the mixture of La and Ce in magnesium were used as starting materials. Each element was weighted at a special ratio with an extra amount for burning loss during melting. During alloy making, a top loaded electrical resistant furnace was used to melt the metal in a steel crucible under protection of N.sub.2+(0.05−0.1)vol.% SF.sub.6. A batch of 10 kg alloy was melted at a temperature of 730° C. each time. After the melt was homogenised in the crucible, a mushroom sample with ϕ60×10 mm testing part for composition analysis was made by casting melt directly into a steel mould. The casting was cut off 3mm from the bottom before performing composition analysis. The composition was analysed using an optical mass spectroscopy, in which at least five spark analyses were carried out and the average value was taken as the chemical composition of the alloy. The actual composition of the alloy was Mg-5.5(La, Ce, Nd, Gd, Y)-0.5Al-0.3Zn-0.3Mn (wt.%), with Be also being present at about 20ppm with balanced Mg.

[0063] After composition analysis, the casting samples were made by a 4500 kN cold chamber HPDC machine, in which all casting parameters were fully monitored and recorded. The pouring temperature was controlled at 700° C., which was measured by a K-type thermocouple. The die to make standard samples for mechanical properties and thermal conductivity were made under the corresponding optimised condition. The dies were heated by the circulation of mineral oil at 250° C. The samples for thermal conductivity were ϕ12×20 mm round bars. The mechanical properties and thermal conductivity were measured following a standard method defined by ASTM.

[0064] A number of other samples were made in accordance with the method of Example 1 using high pressure die casting and gravity and permanent mould die casting. The thermal conductivity was tested under as-cast condition and various temperatures. The thermal conductivity at room temperature is shown in Table 2. The castability was assessed to the commercial A380 and AZ91D alloy and the value in the following Table 2 is a ratio between the filling lengths in permanent mould casting. The thermal conductivity at various elevated temperatures is shown in FIG. 1.

[0065] It can be seen that the magnesium alloy samples which are not in accordance with the invention (Samples 2-4) have a lower thermal conductivity than the reference aluminium alloy (Sample 1). However, the magnesium alloy samples which are in accordance with the invention (Samples 5-8) have a comparable thermal conductivity to Sample 1.

TABLE-US-00001 TABLE 2 Thermal conductivity Castability (20° C., (ratio Sample Alloy composition (wt. %)* W/m .Math. K) value) 1 Al—9Si—3Cu—1Fe (A380**) 110 100 2 Mg—9Al—1Zn—0.2Mn (AZ91D**)  50  95 3 Mg—4Al—3.5Re—0.25Mn—0.2Zn (AE44**)  82  80 4 Mg—3.5Al—4Re—0.3Mn—0.2Zn (AE44**)  85  85 5 Mg—1.5La—1.1Ce—0.9Nd—1.6Gd—0.1Y—0.2Zn—0.5Al—0.3Mn 110  95 6 Mg—1.1La—1.8Ce—1.2Nd—1.5Gd—0.1Y—0.3Zn—0.6Al—0.2Mn 107  90 7 Mg—1.6La—1.2Ce—1.0Nd—1.0Gd—0.1Y—0.2Zn—0.4Al—0.1Mn 105  90 8 Mg—2.1La—1.3Ce—0.8Nd—1.2Gd—0.1Y—0.2Zn—0.5Al—0.3Mn 108  90 *Be also present in amounts of up to 20 ppm **Commercially available alloys

[0066] Turning to FIG. 2, the inventors have tried to test the castability of different alloys with the typical composition disclosed in the art. This is not quantitative method as only relative methods are used in industry. Experiments were carried out to show that the references in Table 1 were not suitable for high pressure die casting and designed for low temperature (<=150° C.) application only, while the alloys of the present invention are suitable for high pressure die casting and could be worked at high temperature (>=200° C.).

[0067] The alloys that were tested were those listed in Table 1 above, and these are identified in

[0068] FIG. 2 as follows:

[0069] (a) CN101113502A, (b) CN101113504A, (c) CN101113503A, (d) CN104046867A, (e) CN102251161A, (f) CN101709418A, (g) CN104152769A, (h) CN102719716A, (i) US20090068053, (j) JP2012197490, (k) CN102560210A, (1) US3094413, (m) the present claimed magnesium alloy with the composition of Mg-1.4La-2.1Ce-0.6Nd-1.2Gd-0.1Y-0.3Zn-0.8Al-0.3Mn.

[0070] From FIG. 2, it is clear that many of existing alloys are not able to make sound castings using high pressure die casting process. However, the casting of the alloy (m) in accordance with the invention is sound, which means the castability of the alloy is very good.

[0071] Turning to FIG. 3, this shows high temperature creep properties of AZ91D (a typical prior art alloy) and a magnesium alloy in accordance with the invention (Mg-1.4La-2.1Ce-0.6Nd-1.2Gd-0.1Y-0.3Zn-0.8Al-0.3Mn). The short dot curve shows the typical creep properties of the AZ91D alloy at 150° C. and 90 MPa (labelled “reference”). The solid curve shows the typical creep properties of the alloy of the present invention (labelled “present”) at 200 ° C. and 100 MPa.

[0072] All optional and preferred features and modifications of the described embodiments and dependent claims are usable in all aspects of the invention taught herein. Furthermore, the individual features of the dependent claims, as well as all optional and preferred features and modifications of the described embodiments are combinable and interchangeable with one another.

[0073] The disclosures in UK patent application number 1905971.6, from which this application claims priority, and in the abstract accompanying this application are incorporated herein by reference. Claims