Effects of particulate reinforcements on the hardness, impact and tensile strengths of AA 6061-T6 friction stir weldments

Abstract

Due to loss of structural strengthening at temperatures beyond 250°C, heat-treated aluminium alloys (e.g. AA 6061-T6) weldments are usually characterized with poor mechanical properties including hardness, tensile and impact strengths. In this work, friction stir weldments of AA 6061-T6 reinforced with the additions of SiC, B4C and Al2O3 particles at the joints were produced and investigated for improved hardness, tensile strength and impact strength over the unreinforced weldment. The results showed that the entire reinforced welded joint exhibited improved hardness because of the enhanced metal matrix grain refinement and inherent high hardness of the reinforcement particles. B4C particle addition produced hardest joint of about 81% of the base metal hardness (∼114 HV0.3). The impact energies of the SiC (16.9 J), B4C (16.5) and Al2O3 (12.2 J) reinforced weldments are closer to that of the base metal (18.6 J) compared with the unreinforced weldment (9.6 J). The reinforced weldments showed no significant improvement over the tensile strength of the unreinforced weldment. B4C and SiC reinforcements produced the highest improvements in the hardness (at the joint) and impact strength of the AA 6061-T6 friction stir weldments, respectively.