Refill Friction Stir Spot Welding Al Alloy to Copper via Pure Metallurgical Joining Mechanism

Zhikang Shen,Xiaochao Liu,Haiyan Chen,Fenjun Liu,Wentao Hou,Adrian Gerlich,Wenya Li,Wei Guo,Yuquan Ding

doi:10.1186/s10033-021-00593-0

Abstract

The current investigation of refill friction stir spot welding (refill FSSW) Al alloy to copper primarily involved plunging the tool into bottom copper sheet to achieve both metallurgical and mechanical interfacial bonding. Compared to conventional FSSW and pinless FSSW, weld strength can be significantly improved by using this method. Nevertheless, tool wear is a critical issue during refill FSSW. In this study, defect-free Al/copper dissimilar welds were successfully fabricated using refill FSSW by only plunging the tool into top Al alloy sheet. Overall, two types of continuous and ultra-thin intermetallic compounds (IMCs) layers were identified at the whole Al/copper interface. Also, strong evidence of melting and resolidification was observed in the localized region. The peak temperature obtained at the center of Al/copper interface was 591 °C, and the heating rate reached up to 916 °C/s during the sleeve penetration phase. A softened weld region was produced via refill FSSW process, the hardness profile exhibited a W-shaped appearance along middle thickness of top Al alloy. The weld lap shear load was insensitive to the welding condition, whose scatter was rather small. The fracture path exclusively propagated along the IMCs layer of Cu9Al4 under the external lap shear loadings, both CuAl2 and Cu9Al4 were detected on the fractured surface on the copper side. This research indicated that acceptable weld strength can be achieved via pure metallurgical joining mechanism, which has significant potential for the industrial applications.

Highlights

In order to obtain technical and economic advantages, joining of dissimilar materials is gaining wide popularity in the industries [1,2,3,4]
While the thickness of the intermetallic compounds (IMCs) layer attached to the bottom copper sheet was approximate 0.5 μm thick, where the average chemical component was 27.7%Al and 72.3%Cu, consistent with that of C u9Al4 according to Al-Cu phase diagram
4 Conclusions In this investigation, interfacial microstructure and mechanical performance of Al/copper dissimilar refill friction stir spot welds were systematically evaluated in terms of interfacial microstructure, hardness profile, lap shear load and failure mechanism

Summary

Introduction

In order to obtain technical and economic advantages, joining of dissimilar materials is gaining wide popularity in the industries [1,2,3,4]. It is a critical issue to fusion join Al alloy to copper since they can produce thick and continuous intermetallic compounds (IMCs) [6, 7]. Mechanical joining approaches such as self-piercing riveting can Compared to conventional and pinless FSSW, mechanical performance of refill FSSWed joint can be dramatically improved by increasing the weld effective bonded volume and integrity [18]. A tool comprises a clamping ring, a sleeve and a pin is applied during refill FSSW, the weld is fabricated by plasticizing, Shen et al Chin.

Methods

Results

Conclusion