Effect of laves phases on high-temperature tensile strength for a Mg-Al-Ca-Mn alloy

The effect of Laves phases (C15-Al2Ca, C36-(Mg, Al)2Ca) on tensile strength was investigated for the Mg-5.0Al-1.5Ca-0.3Mn alloy produced by die-casting. The die-cast specimen was aged at 523 K for 10 h to precipitate the C15 phase within the α-Mg grains, and the aging treatment at 623 K for 100 h was carried out to divorce the interconnected skeleton of C36 phase. The tensile tests were conducted at temperatures between 298 and 473 K. The superior tensile strength is obtained for the as die-cast and 523 K/10 h-aged specimens relative to the 623 K/100 h-aged specimen at 473 K. The interconnected skeleton of C36 phase acts as a barrier of dislocations which glide in the α-Mg grains, and prevents the dislocation recovery at dendrite boundaries during high-temperature deformation. The precipitation of the C15 phase within the α-Mg grains increases the tensile strength at temperatures below 373 K, while it is not effective to enhance the tensile strength at 473 K. It is deduced that dislocations are easy to climb and overcome the C15 precipitates at 473 K, while the dislocation climb is negligible below 373 K.