Effects of Processing Parameters on the Microstructures and Mechanical Properties of In Situ (Al3Ti + Al2O3)/Al Composites Fabricated by Hot Pressing and Subsequent Friction-Stir Processing

Abstract

In situ (Al3Ti + Al2O3)/Al composites were fabricated in an Al-TiO2 system by the combination of hot pressing (HP) and friction-stir processing (FSP). The effects of HP and FSP parameters on the microstructures and mechanical properties of the in situ composites were studied. The Al-TiO2 reaction extent increased with increasing the temperature and holding time of HP. Subsequent FSP not only induced Al-TiO2 reaction, resulting in the formation of nanosized Al3Ti and Al2O3, but also rounded the polygonal Al3Ti particles formed during HP. The tensile strength of the FSP sample in which the Al-TiO2 reaction took place completely during HP was lower than that of the FSP samples in which the Al-TiO2 reaction took place hardly or partly during HP. For the FSP samples in which the Al-TiO2 reaction took place hardly during HP, the volume fraction of reinforcing particles increased with decreasing the traverse speed, resulting in the increase in tensile strength of the FSP samples. At a traverse speed of 25 mm/min, increasing the rotation rate from 1000 to 2000 rpm produced little influence on the microstructures and mechanical properties of the in situ composites. Additional 2-pass FSP in water refined the matrix grains, resulting in the significant increase in the tensile strength.