Study on the Microstructure and Mechanical Properties of ZrB2/AA6111 Particle-Reinforced Aluminum Matrix Composites by Friction Stir Processing and Heat Treatment

In this paper, the Al-K2ZrF6-KBF4 reaction system, a melt reaction method, was used to prepare in situ ZrB2/AA6111 particle-reinforced aluminum matrix composite. The modification of friction stir processing (FSP) and T6 heat treatment (HT) was carried out for this composite for the first time. The reinforcing particles in the stirring zone after FSP+HT were refined from 1.7-1.9 to 0.1-0.3 mu m. The grain size was refined from 10-50 to 2-5 mu m and then slightly coarsened to 3-10 mu m. The tensile strength of the FSP stirring zone is 193.40 MPa, the elongation is 29.33%, and the average hardness is 60 HV. The hardness of the stirring zone is not uniform and fluctuates in a large range of 53-80 HV. After the T6 heat treatment, the tensile strength of the stirring zone increased by 63.8% to 316.75 MPa. The tensile strength was 13% higher than that of T6-6061. The elongation remained at 30.12% and did not decrease. The elongation is 10% higher than that of other 6xxx aluminum alloys and composites after T6 heat treatment. The plasticity-reduction of the conventional alloy after T6 heat treatment was solved. The property is more uniform and the average hardness is 120 HV. Calculated by the theoretical model, the yield strengths of the stirring zone of the original composite, FSP, and FSP+HT composites were more than 96% consistent with the experimental values.