Influence of Preheating Temperature on Cold Metal Transfer (CMT) Welding–Brazing of Aluminium Alloy/Galvanized Steel

Youqiong Qin,Wenxiang Jiang,Xi He

doi:10.3390/app8091659

Abstract

Bead-on-plate cold metal transfer (CMT) brazing and overlap CMT welding–brazing of 7075 aluminium alloy and galvanized steel at different preheating temperatures were studied. The results indicated that AlSi5 filler wire had good wettability to galvanized steel. The preheating treatment can promote the spreadability of liquid AlSi5. For the overlap CMT welding–brazed joint, the microstructure of the joint was divided into four zones, namely, the interfacial layer, weld metal zone, zinc-rich zone, and heat affected zone (HAZ). The load force of the joints without preheating and 100 °C preheating temperature was 8580 N and 9730 N, respectively. Both of the joints were fractured in the fusion line with a ductile fracture. Further increasing the preheating temperature to 200 °C would decrease the load force of the joint, which fractured in the interfacial layer with a brittle fracture.

Highlights

The growing demand for lightweight design in the automotive industry arises a strong interest in the joining of aluminium alloy to steel
The Fe atoms diffused into the melted metal, and intermetallic compound (IMC) was formed at the interface of the steel/brazing metal
The width of the wetting length increased and the wetting angle decreased with the increasing preheating temperature

Summary

Introduction

The growing demand for lightweight design in the automotive industry arises a strong interest in the joining of aluminium alloy to steel. It is difficult to obtain a sound joining of aluminium to steel because of the large differences in the melting points, the coefficient of the thermal conductivity, and thermal expansion, especially the formation of intermetallic compound (IMC) at the Fe/Al interface. The total thickness of the IMC was primarily dominated by thermal diffusion and was related to the thermal cycle (i.e., peak temperature and duration) of the welding process [6]. It was a preferable method to join aluminium alloy and steel, as it could suppress the growth of IMC and obtain good mechanical properties of Al/Fe joint. In this process, part of the aluminium alloy was melted, but the steel was in a solid state. The Fe atoms diffused into the melted metal, and IMC was formed at the interface of the steel/brazing metal

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Conclusion