Effect of Ni addition on microstructure and mechanical properties of Al–Mg–Si–Cu–Zn alloys with a high Mg/Si ratio

The effect of adding 0.03wt%Ni on the microstructure and mechanical properties of Al–Mg–Si–Cu–Zn alloys was systematically studied.The results reveal that the number density of spherical Fe-rich phases within grains increases with the addition of Ni,accompanied by the formation of Q(Al3Mg9Si7Cu2)precipitates around the spherical Fe-rich phases.Additionally,Ni addition is beneficial to reducing the grain size in the as-cast state.During the homogenization process,Q phases could be completely dissolved and the grain size could remain basically unchanged.However,compared with the Ni-free alloy,the Fe-rich phase in the Ni-containing alloy is more likely to undergo the phase transformation and further form more spherical particles during homogenization treatment.After thermomechanical processing,the distribution of Fe-rich phases in the Ni-containing alloy was further greatly improved and directly resulted in a greater formability than that of the Ni-free alloy.Accordingly,a reasonable Ni addition positively affected the microstructure and formability of the alloys.