Microstructural evolution and mechanical property of Al–Mg–Mn alloys with various solidification cooling rates

Abstract

In the present work, the microstructural evolution and mechanical property of as-cast Al–6 Mg–0.8Mn alloys with respect to the solidification cooling rate was investigated. The results demonstrate that as the cooling rate increases from 0.5 K/s to 46.9 K/s, the average grain size decreases firstly and then increases slightly; the average secondary dendrite arm spacing, the average length of Al 6 Mn and Al 3 Mg 2 phases decreases. A high cooling rate (21.3 K/s and 46.9 K/s) causes the increase in the solute segregation/shrinkage porosities, and a low cooling rate (0.5 K/s) leads to the formation of casting defects, thus deteriorating the mechanical properties of alloys. The alloy with the cooling rate of 5.4 K/s shows an optimum mechanical property i.e., the tensile strength, yield strength, and elongation are 298.7 MPa, 133.8 MPa, and 30.5%, respectively. The enhanced strength-ductility synergy is mainly attributed to the refined secondary dendrite arm spacing and reduced casting defects. This work provides a reference for the fabrication of as-cast Al–Mg–Mn alloys with excellent mechanical performance. • The relationship between cooling rate and microstructure/property was established. • The variation in tensile property due to the microstructural evolution was discussed. • The microstructural evolution induced by cooling rate was analyzed. • The strength-ductility synergy associated with the cooling rate was revealed.