Investigation of the Critical Factors Influencing Mechanical Properties and Failure Behavior in Weld-Brazed ZnAlMg Coated Steel

The non-fusion weld-brazing method has gained attention in automotive manufacturing, particularly for joining zinc-coated steels, due to its reduced heat input and resulting decrease in welding defects such as cracking and warping. However, despite extensive research, a significant gap persists in understanding how various characteristics of weld-brazed joints impact their mechanical properties. This study aims to investigate the key factors influencing the mechanical properties and failure behavior of weld-brazed zinc-aluminum-magnesium (ZnAlMg) coated interstitial free (IF) steel. Two weld-brazing procedures, differing in heat input, were employed to develop brazed joints with varying bead geometries, microstructures, and interfacial layer thicknesses. Results indicate that while the sample with higher heat input exhibited a larger bead size, higher precipitate density, and thicker interfacial layer, its peak load during shear-tensile testing was identical to that of the other specimen. However, the joint with lower heat input showed greater extension during mechanical testing. This study showed that bead characteristics alone proved insufficient for predicting the mechanical behavior of welded-brazed joints. Experimental and numerical strain distribution analysis revealed that weld-brazed joint characteristics directly influence the distribution of applied loading across different regions of the joint. The specimen with a larger bead size and higher precipitate density exhibited lower degrees of rotation during loading, leading to higher localized strain at the base metal, necking, and failure. These findings clarify the uncertainty surrounding the correlation between weld-brazed characteristics and mechanical properties. By identifying a significant factor influencing joint mechanical properties, this study advances the application of weld-brazing technology in joining zinc-coated steels within the automotive industry.