Study on Coating Melting Behavior on Weld Growth Mechanism for Al-Si coated Hot-Stamped Boron Steels in Resistance Spot Welding

Abstract

The effect of coating melting behavior on nugget growth during resistance spot welding of hotstamped boron steels was evaluated. A comparative analysis of the dynamic resistance for bare hot stamped and Al-Si coated hot stamped boron steels was carried out. The dynamic resistance curve of Al-Si coated hot stamped boron steel was higher than bare hot stamped boron steel during the whole stages of weld time. Higher α-peak and β-peak for Al-Si coated hot stamped boron steel resulted in larger nugget size at higher than 4.0 kA weld current owing to non-linear layer structure of alloyed coating, which appears to restrict the current passage through the faying interface. In the case of Al-Si coated hot-stamped boron steel, most of the Al-Fe intermetallic coatings are expected to be pushed away while in the liquid state at the faying interface. The pressure build up during the early stage of weld pushes the liquid Al-Fe intermetallic coating towards the edge of the faying interface. The continuous liquid state of Al-Fe intermetallic through the faying interface ensures the large contact area for the current passage to enlarge the nugget diameter. †(Received June 1, 2014)