Development of Magnesium-Rare Earth Die-Casting Alloys

An overview of the development of a high-performance Mg-RE based alloy, HP2+, is presented, which has a good combination of die-castability and mechanical properties at ambient and elevated temperatures. The original alloy, HP2, was a die-casing version of the sand-cast alloy SC1 developed for powertrain applications. However, HP2 tended to crack substantially, leading to unusable castings due to its high Nd content. It was found that the solidification path of Mg-RE alloys can be engineered to reduce the propensity to hot tearing by changing the mixture of RE elements towards La-rich, which leads to an increase in the amount of eutectic and a reduction of the solidification range. Precipitate-forming RE elements, such as Nd or Y, were optimized for HP2+ to meet the requirement for high temperature creep resistance. Whilst some challenges remain with the commercial application of HP2+, the learnings from the alloy design process can be applied to other alloy development programs.