Inhibiting creep in fine-grained MgAl alloys through grain boundary stabilization

The limited creep resistance of wrought MgAl alloys restricts their lightweight applications at intermediate temperatures due to the softening effect of discontinuous precipitation (DP) on the dislocation-controlled creep. Here, we developed a creep-resistant wrought MgAl alloy through microalloying of Y and Ca. The resulting alloy exhibited an order of magnitude enhancement in the creep resistance at 125 ℃/50–100 MPa. In contrast to the grain boundary instabilities by DP in the previously reported wrought MgAl alloys, we show that the addition of 0.21Y+0.15Ca wt% produces a (Zn+Ca) co-segregation at the grain boundaries as a result of their segregation energy and the activation energy of grain boundary migration, thereby stabilizing the grain boundaries. The (Zn+Ca) co-segregation inhibits the dynamic DP and promotes the formation of intragranular Al-enriched clusters, which favorthe formation of Al2Y, Mg17Al12 nano precipitates, thereby impeding intragranular dislocation motion during creep. Furthermore, the addition of 0.21Y+0.15Ca wt% facilitates the formation of a fine and uniform recrystallization structure in the microalloyed alloys compared to AZ80 due to the high activation energy of mobility for the (Zn+Ca) segregated grain boundary. Therefore, the microalloyed alloys exhibit good tensile properties with 380 MPa tensile strength and 18 % elongation. Our constitutive analysis revealed that the (Y+Ca) microalloying decreased the creep stress exponent by 29 % and increased the creep resistance in the medium to high-stress range. Microalloying provides a promising way to develop low-cost creep-resistant wrought MgAl alloys.