Assessing profile damage of uncoated and AlTiN coated FSW tools after successive travel on AA6061-T6 plate

Abstract

The quantitative assessment of profile damage of square (SQ) and threaded with three intermittent flat faces (TIF) tool pin was appraised and presented for both uncoated and AlTiN coated tools during friction stir passes on AA6061-T6 plates successively after different travel lengths. Significantly lower profile damage with small amount of profile twisting was noted for TIF tool pin as compared to the SQ tool pin owing to lower force and torque, as predicted by finite element (FE) results. For AlTiN coated tools, the pin profile damage reduced significantly due to high wear resistance, hardness and good adhesion of coating with the tool substrate. Significantly lower temperature rise was noted in the AlTiN coated tool compared to the uncoated tool. A mathematical approach to predict the heat generation was presented and predicted temperatures were found in good agreement with FE results. Plastic deformation of sharp corners, adhesion and abrasion wear of flat faces, and initiation of crack near tool pin-shoulder interface was noted in uncoated tools however, they got reduced in the AlTiN coated tool. The delamination of coating near the tool pin edge, flat surfaces and near the tool pin-shoulder interface was noted due to dislodging of adhered work material. Fairly uniform tensile strength and flexural load were obtained after different weld lengths for AA6061-T6 FSW joints prepared with the AlTiN coated TIF tool pin.