A New Design for Friction Stir Spot Joining of Al Alloys and Carbon Fiber-Reinforced Composites

Abstract

Friction stir spot welding (FSSW) has been recently developed to join dissimilar materials. However, the traditional requirement for a rotating tool consists of a pin and shoulder in FSSW leads to a complex joining process and unpredictable defects. In this study, a new static-shoulder design in FSSW was proposed and developed to join Al alloys to carbon fiber-reinforced polymer (CFRP) composites. The main joining parameters, including pin rotational speed, pin feed rate and pin plunge depth, were varied to investigate their effects on the joining temperature, materials interaction and the strength of joints. The pin rotational speed had the largest influence on the joining temperature. Lap shear tensile testing was conducted to evaluate the performance of the joints. The joints exhibited the ultimate lap shear force from 230 to 260 N. A brittle fracture occurred with the displacement-at-fracture load of 0.35-0.41 mm. Cross-sectional images revealed the creation of undulations on the surface of Al alloys in the joining zone. The undulations created a macro-mechanical interlocking bonding between the materials, which determined the performance of the joints. For a flat pin, by increasing the plunge depth from 1.25 to 1.30 mm, the undulation size increased from 0.21 to 0.26 mm, which can enhance the macro-mechanical interlocking bonding between Al alloys and CFRP and accordingly increased the ultimate shear force of the joints from 230 to 241 N. Use of a fluted pin significantly influenced the flow of the plasticized Al alloy which created pronounced undulations and large Al alloy spikes of 0.46 mm. These features seemed to establish an efficient macro-mechanical interlocking bonding, which resulted in a noticeable improvement in the performance of the joint. For a plunge depth of 1.30 mm, the ultimate shear force increased to 261 N using the fluted pin.

A Review on the Recent Trends in Forming Composite Joints Using Spot Welding Variants

“…Refill FFSW, even though it gives an improved weld strength compared to FFSW, is considered an expensive and complex process, as the tool has three separate components that need to be controlled [150]. In FFSW, the reduced weld strength is mainly due to weld thinning, keyhole defects, and hook defects [151,152]. Other variations in the FFSW techniques reported for joining metal-polymer composite joints are threaded hole friction stir spot welding (THFSSW) [153,154], static shoulder friction stir spot welding (SSFSSW), and pinless friction stir spot welding (PFSSW) [151,155].…”

“…In FFSW, the reduced weld strength is mainly due to weld thinning, keyhole defects, and hook defects [151,152]. Other variations in the FFSW techniques reported for joining metal-polymer composite joints are threaded hole friction stir spot welding (THFSSW) [153,154], static shoulder friction stir spot welding (SSFSSW), and pinless friction stir spot welding (PFSSW) [151,155]. Studies on RSW, FSSW, PFSSW, and THFSSW (at times referred to as pre-hole FSSW (PHFSSW)) have shown that FFSW gives a better weld strength and has more flexibility in joining aluminum alloys and polymer composites yet is far more expensive compared to RSW, as shown in Figure 21 below.…”

Review on the advancements and relevance of emerging joining techniques for aluminium to polymers/carbon fibre-reinforced polymer lightweight hybrid structures

“…139 A static shoulder FSpJ tool with a fluted tool increased the mechanical interlocking of the Al-CFRP joint. 140 FSSW used a hybrid HCl immersion and salinization treatment to generate a high-strength Al/ CFRTP joint. Dendritic nanostructures were created by immersing an Al surface in HCl, resulting in mechanical interlocking and enhanced wettability.…”

In-Plane Shear Strength of Single-Lap Co-Cured Joints of Self-Reinforced Polyethylene Composites

“…The resulting joints are responsible for ensuring effective load transfer between parts, thus maintaining the integrity of the linked components [ 46 ]. For composites, there are two main joining methods: mechanical fastening (which infers undesired and prejudicial stress concentration spots and an overall weight increase caused by additional fasteners [ 47 ]) and adhesive bonding (which provides load transfer with more uniform distribution over larger areas) [ 48 ]. Adhesive bonding may be performed by secondary bonding, involving the usage of adhesives between the parts [ 49 , 50 ], or by co-curing, where the matrix of the composite is cured in contact with the desired adherend and, hence, cure and bonding happen simultaneously.…”