Improvement of the mechanical performance of ZnAlMg coated steel brazed joints through precipitation-based strengthening

Abstract

The non-fusion weld-brazing process has attracted considerable attention in the automotive industry due to its lower susceptibility to welding-related defects and high capability to join similar and dissimilar materials. However, the mechanical performance of the brazed joint is limited to the strength of the filler material, which restricts the widespread adoption of this technique in the automotive industry. The objective of the present study is to investigate a viable and effective solution for enhancing the local mechanical properties of the braze bead through the in-situ formation of precipitates during weld-brazing of ZnAlMg coated steel. The results showed that increasing heat input led to the dilution of molten filler material (i.e., CuSi3Mn alloy) by the steel substrate, resulting in the formation of a high number density of FeSi(Cu) precipitates with irregular morphologies within the braze bead. Analysis of cyclic load-depth indentation measurements within the braze bead revealed that the presence of FeSi(Cu) precipitates led to a considerable improvement of mechanical properties in the local region of the braze bead. Ultimately, this resulted in higher resistance of the braze bead to cracking as well as greater structural integrity when subjected to non-uniform deformation (such as rotation) during shear-tensile loading. The results also showed that the increased heat input led to optimized joint geometry and improved bonding of joint interfaces, further contributing to the improving mechanical properties of the joint. This study introduces a novel approach to the development of highly robust braze joints through the use of a precipitation-based strengthening mechanism. This approach offers an effective solution to extend the scope of the brazing process for joining high/ultra-high-strength materials used in the automotive industry.