Effect of SiC interlayer on microstructure and joint strength of Cu-Al welds obtained using a new friction processing method.

A novel friction processing method is used to join Al-Cu sheets in lap configuration without any significant deformation or thickness depletion of parent metals. A pin less, flat shouldered tool is rotated and plunged against a sacrificial top sheet to initiate localised melting at the joint interface. Effect of addition of SiC particles at the joint interface on resulting weld microstructure, interface strength, and joint electrical resistance is studied in this work. Diffusion reaction of SiC particles with Al and Cu results in melting of the interface at around 530 °C. The peak temperature in weld zone with SiC particles is significantly lower than the Al-Cu eutectic temperature and melting points of Al, Cu. Cross-sectional scanning electron micrographs, fractographs, electron dispersive spectroscopy, X-ray diffraction, lap shear, T peel tests, and joint electrical resistance measurements are used to investigate pure Al-Cu and Al-SiC-Cu weld joints for different SiC particle concentrations. SiC particles are found to enhance joint strength through generation of fine eutectic microstructures with sub-micron lamellar spacing and through formation of uniformly distributed nano-precipitates. The highest peel strength achieved with the SiC interlayer is around 70 % higher than that for corresponding pure Al-Cu welds. Despite formation of thick hypereutectic region towards Cu side, with larger volume percentage of "lumps of intermetallics", there is a clear diversion of fracture path from the intermetallics rich region towards the SiC-eutectic boundary of the interface region in Al-SiC-Cu welds. Additionally, SiC interlayer is seen to result in lower percentage rise in joint resistance with temperature. However, SiC interlayer results in a marginal increase in joint electrical resistance. Thus, addition of SiC particles at Al-Cu joint interface is recommended for significantly enhancing the joint strength with no significant change in joint electrical resistance. [Display omitted] • Diffusion of Si from SiC particles into Al-Cu melt reduces the interface melting temperature. • SiC particles expose nascent surfaces of Al-Cu, promote interdiffusion and enhance wetting. • Nanoprecipitates are seen to form in the ''crumbled" eutectic melt region. • SiC particles increase the fracture energy with a highly jagged fracture surface. • Joints with SiC interlayer exhibit higher joint strength at nearly similar electrical resistance. [ABSTRACT FROM AUTHOR]