Development of high thermal conductivity, enhanced strength and cost-effective die-cast Mg alloy compared with AE44 alloy

The thermal conductivity (TC) and strength trade-off has been a long-standing dilemma for developing high TC alloys. Here a novel high TC and cost-effective die-cast Mg2.8Al3.8La0.4Nd alloy was developed with enhanced yield strength (YS) at room temperature (RT) and high temperatures (HT), compared with the commercially widely used die-cast AE44 magnesium alloy. The new alloy provided the TC of 104.0 and 125.9 W/(m·K) separately at RT and 300 °C. Compared with AE44 alloy, the TC was improved by ∼13.5%. The new alloy also delivered an excellent YS of 137.1 MPa, ultimate tensile strength (UTS) of 240.2 MPa and elongation of 8.8% at RT, and the YS of the new ally was enhanced by 6.3% at RT and 9.8% at 300 °C, compared with AE44 alloy. The new alloy only has a 1.3% increase in raw material cost compared with AE44 alloy, offering a relatively cost-effective alternative. The lamellar (Al,Mg)3RE and Al11RE3, the needle-like Al2.12RE0.88 and the blocky Al10RE2Mn7 intermetallic phases were identified. With the optimizing addition of Al and La, the Al solute amount in the matrix was reduced remarkably by 42% and then contributed to the improvement of TC. The major (Al,Mg)3RE phase at grain boundaries (GBs) contributed heavily to the enhancement of YS. This study elucidates the importance of the transfer of Al from the matrix to form higher content and novel Al-based intermetallic phases at GBs, for achieving die-cast Mg-Al-based alloys with excellent TC and strength.