The effect of Mg content on microstructure in Al-12wt. %Zn-x Mg Alloy

The effect of adding different Mg contents to an Al-12wt.%Zn master alloy was experimentally investigated. The Al-Zn-Mg alloys were unidirectionally solidified as a function of solidification parameters, temperature gradient G(L), solidification front velocity V, and composition C(0). The alloys were solidified with a constant temperature gradient (G(L)=2500K/m) in the solidification front velocity range from 4x10(-6)m/s to 1.7x10(-4)m/s. The resulting microstructure was characterized to investigate the effect of solidification front velocities and composition on primary dendrite arm spacing, volume percentage of eutectic in interdendritic regions and tau intermetallic phase in alpha-Al matrix. Theoretical models for the dendrite arm spacing and dendrite tip radius have been compared with the experimental observations.