Role of Eutectic Intermetallic Phase on Creep Strength in a Die-Cast Mg-Al-Ca Alloy: Evaluation by Internal Stress Measurement

摘要

The internal stress during high temperature creep was investigated for a die-cast Mg-Al-Ca alloy AX52 (X representing calcium) at 473 K through the strain-transient dip test technique. The microstructure of the alloy is characterized by the eutectic intermetallic phase covering the primary alpha-Mg grains. The eutectic intermetallic phase plays dual roles in enhancing the creep strength from the viewpoint of the internal stress. First, the eutectic intermetallic phase sustains the stress-independent component of the internal stress with the magnitude of 15 MPa, resulting in the decrease in the effective stress. And second, it lowers the creep rate by two orders of magnitude at a given effective stress by reducing the mobile dislocation density and/or glide velocity of dislocations.