# The Role of Element Segregation in the Fracture Mechanism and Performance of Spot-Welded AlSi7MnMg Aluminum Alloy Joints

## TL;DR

This paper studies how element segregation affects the strength and fracture behavior of spot-welded aluminum alloy joints.

## Contribution

The study reveals how element segregation and secondary phases impact the welding process window and joint performance in non-heat-treatable aluminum alloys.

## Key findings

- Weld nuggets show a dual structure with columnar and equiaxed grains and an 'M'-shaped hardness profile.
- Segregation of Si, Fe, and Mn leads to eutectic regions and microporosity, causing cracks and narrowing the welding window.
- Non-equilibrium solidification explains the microstructure and solute behavior affecting joint performance.

## Abstract

This study systematically investigates the microstructural characteristics and mechanical properties of resistance spot-welded joints in 3 mm thick non-heat-treatable die-cast AlSi7MnMg alloy, with particular focus on the influence of element segregation and secondary phase behavior on fracture mechanisms and the process window. The results indicate that the weld nugget exhibits a typical dual structure consisting of columnar and equiaxed grain zones, with a corresponding “M”-shaped microhardness profile. Significant segregation of Si, Fe, and Mn elements at the nugget boundary was observed, leading to the formation of low-melting-point eutectic regions and secondary phase bands. These features induce microporosity along segregation trajectories, serving as crack initiation sites and resulting in a notably narrowed spot welding process window. From the perspective of microstructure and solute behavior during non-equilibrium solidification, this work elucidates the intrinsic mechanisms governing joint performance and process stability in non-heat-treatable die-cast aluminum alloys, providing a theoretical basis for their engineering applications.