Study on the thermal assistance friction stir lap welding of aluminum alloy and CFRTP

Abstract With the rapid development of transportation and electronic equipment industries, lightweight requires reliable joining technology for metal/polymer. Preheating before welding is a potential way to improve the tensile properties of the joint and reduce the risk of defect formation. In this study, thermal assistance friction stir lap welding (TA‐FSLW) in joining 6061‐T6 aluminum alloy and carbon‐fiber‐reinforced thermoplastic (CFRTP) is investigated. The welds are evaluated by OM image segmentation and statistical calculation, temperature detection in thermal imaging, SEM and EDS of the fracture, tensile, and hardness analysis. From the quantitative analysis results of the width of the CFRTP side‐melting zone and the area of Al alloy fragments in the welding zone, the movement of the polymer chain in the CFRTP of joint is intensified by thermal assistance, which reduces the thickness of the melting zone on the side of the composite material. The area of metal fragments ranges from 100 to 2 × 10 ⁶ μm ² . The microscopic analysis results indicate that preheating enhances the initial thermal motion of molecules. Gaseous polymers are dissociated from the molten state, reducing the number of bubbles in the composite material. Small size fragments are inserted into the molten CFRTP and mechanical interlocking is enhanced due to the uniform interweaving of metals and polymers. A maximum tensile strength of 39.97 MPa is achieved, which increases by 37.6% compared with the conventional FSLW. Highlights Thermal assistance friction stir welding technology is applied to the welding of aluminum alloy with carbon‐fiber‐reinforced thermoplastic. The number and area of aluminum alloy fragments are counted and analyzed by the metal segmentation counting algorithms. Thermal assisted technology reduces the thickness of the melting zone of CFRTP and enhances the material flow and refinement of aluminum alloy fragments.