The Effect of Rare Earth Mischmetal on the High Temperature Tensile Properties of an A356 Aluminum Alloy

摘要

Aluminum-silicon (Al-Si) based alloys are prominently used in the transportation industry, due to their impressive strength, great castability, and lightweight properties. Small additions of magnesium (Mg) can improve the mechanical properties through precipitation of strengthening intermetallics such as Mg_2Si. However, the poor thermal stability of Mg_2Si restricts the use of Al-Si-Mg alloys, such as A356, to only lower temperature applications (i.e. less than ～170°C). With the growing demand for increasing fuel efficiency amongst the transportation industry (achieved through elevating the operating pressure and temperature of combustion engines), it is necessary to investigate methods of improving the thermal stability and mechanical properties of the well-established A356 alloy. Addition of rare earth (RE) to Al alloys can improve the thermal stability through precipitation of fine Al-RE intermetallics. Thus, this paper characterizing the effects that RE mischmetal has on the elevated temperature strength and ductility of the A356 alloy. The precipitation of AlSiRE and Al_(20)Ti_2RE intermetallics in the RE modified A356 alloy resulted in a 133% increase in the yield (YS) and tensile (UTS) strength at 250°C and a 158 and 268% increase in YS and UTS at 300°C. Moreover, the T6 A356+3.5%RE alloy retained more than 50% of its strength when increasing the temperature from 250 to 300°C.