Effect of Laser Melting Process on a Modified AA7075 Alloy with Ti-B-Zr Modifiers

Using the Al-Zn-Mg-Cu alloys for the laser melting processes is a challenge due to the formation of hot cracks and pores in the fusion zone. This challenge can be solved by refining the grains, which was achieved in this study. The investigated alloy was modified with 0.5Ti + 0.1B and various Zr concentrations. The microstructure and hardness were studied in the as-cast and pulsed laser melt states (PLM). In the as-cast state, the grains size was reduced 12 times due to forming TiB2 and Al-3(Ti, Zr) as heterogeneous nucleation centers. Increasing Zr content to 0.5% led to an increase in the hardness of the base metal to 136.4 HV. After PLM, the microstructure was changed; at low Zr content, large columnar grains were formed. The columnar grains were eliminated when increasing the Zr content, forming small equiaxed grains at the center. Moreover, the hardness of the laser melted zone at low Zr content decreased to 80.5 HV while increasing Zr content to 0.5 wt.% increased the hardness to 99.3 HV. Thus, adding these elements to the investigated alloy improves their properties for high laser power applications.