Effect of Ca and Sr on the compressive creep behavior of Mg–4Al–RE based magnesium alloys

• Steady state creep rate of AE41 decreases with increasing Ca and Sr concentration.
• Steady state creep rate of AE41 is 11.4 × 10−7 mm/s, and decreased to 1.4 × 10−7 mm/s of AECJ411202.
• The precipitation of AECJ411202 consists of Al2Nd, (Mg, Al)2Ca and Al4Sr.
• Creep resistance is proved by hindering dislocation climbing and grain boundary sliding.

The compressive creep behavior of Mg–4Al–RE–1.2Ca (AEC4112) alloy and Mg–4Al–RE–1.2Ca–0.2Sr (AECJ411202) alloy is investigated on a special apparatus. The stress exponent n under different stresses and the creep activation energy Qc under different temperatures of AEC4112 alloy and AECJ411202 alloy are estimated by an empirical equation. The results reveal that the compressive creep resistance of Mg–4Al–RE (AE41) alloy is improved significantly by a small amount of Ca and Sr. The steady state compressive creep rates of AEC4112 alloy and AECJ411202 alloy are increased with increasing temperature and applied stress. The steady state compressive creep rates of AEC4112 alloy and AECJ411202 alloy are 2.2817 × 10−7 mm/s and 1.3041 × 10−7 mm/s under 150 °C and 100 MPa, respectively. The compressive creep resistance is improved by intermetallic compounds Al2Ca, Al2RE and Al4Sr inhibiting the climbing of the dislocation, the sliding and diffusion of the grain boundary. The compressive creep constitutive equations of AEC4112 alloy and AECJ411202 alloy are written as ε̇s1 = 2.0276 × 10−10 × σ5.662exp(−47447/RT  ) and ε̇s2 = 5.8208 × 10−11 × σ6.123exp(−68252/RT) respectively. The compressive creep mechanism of AEC4112 alloy and AECJ411202 alloy is the combined effects of grain boundary diffusion and grain boundary sliding determined by dislocation climbing.