The Effect of Heat Treatment on the Microstructure and Mechanical Properties of Al/Al3Zr + Al3Ti In-situ Hybrid Composite Fabricated by Friction Stir Processing

In this research, an in-situ hybrid composite reinforced by Al3Zr and Al3Ti aluminide particles was fabricated by friction stir processing (FSP). The base metal was in the form of a rolled Al 3003-H14 alloy sheet, and zirconium and titanium metal powders were used as the reinforcements. Six passes of FSP were applied. Tensile strength and hardness of the base metal, as well as FSPed samples before and after applying heat treatment, were determined. Microstructural examinations were performed using optical and scanning electron microcopy (SEM), and phase formation was identified by X-Ray diffraction. Microstructural examination revealed that by applying FSP, the prior large and elongated grains of the base metal were converted to the fine and equiaxed grains. It was also observed that chemical reactions occurred at the interface between the aluminum matrix and the metallic powders, forming in-situ aluminides of Al3Zr and Al3Ti. The post annealing heat treatment activated these solid state chemical reactions and more aluminides were formed. It was also found that the heat treated hybrid composite possessed the highest tensile strength and hardness values. The tensile strength in such samples reached 195 MPa, as compared to 110 MPa of the base metal.