The researchers improved the mechanical properties of aluminum/steel joints

The researchers of Shanghai Institute of Optics and Precision Machinery, Chinese Academy of Sciences conducted experimental research on resistance laser spot welding technology of aluminum/steel dissimilar metals, and improved the mechanical properties of aluminum/steel welded joints. The research was published in Materials&Design.

Graphic summary. Source: DOI: 10.1016/j.matdes.2022.111022

In order to improve the poor performance of aluminum/steel dissimilar metal welds, researchers used resistance laser spot welding technology to weld the combination. Resistance spot welding connection technology is adopted for spot welding, which is the mainstream technology in the automobile manufacturing industry. Laser flight welding technology is used for circular welding around the spot welding.

Welding process, electrode morphology and current density distribution of RSW: (a) Schematic diagram of typical RSW process; (b) And (c) are the surface and cross section morphologies of the designed electrodes on the steel side and aluminum side, respectively; (d) And (e) are the current density distribution diagrams of the initial stage and the stable stage of the welding process respectively; (f) And (g) are the surface morphology of the weld on the steel side and aluminum side, respectively.

The researchers found that the mechanical properties of aluminum/steel joints were significantly improved by changing the joint structure and controlling the thickness of brittle intermetallic compounds. Resistance spot welding has considerable tensile shear load, but due to the existence of weak bonding zone around the joint, the ductility and energy absorption are poor, which is conducive to crack initiation and rapid growth. The following laser spot welding process is carried out in the weak bonding area of resistance spot welding joints, which inhibits the rapid propagation of cracks along the bonding interface and avoids interface fracture.

Sample size for tensile shear and cross tensile tests: (a) TST sample; (b) CTT samples.

Aluminum/steel dissimilar metal welding technology has broad application prospects in the field of automobile lightweight. However, due to the huge difference in the thermophysical properties between aluminum and steel, a large number of brittle intermetallic compounds and cracks are formed in the weld after welding, resulting in the aluminum/steel joint being unable to meet the application requirements of the vehicle body.

So far, many published works mainly focus on the optimization of welding parameters and cutting of alloy elements in the weld, aiming to reduce the formation of brittle intermetallic compounds in the weld and improve the mechanical properties of the joint. This work provides a new technical solution for aluminum/steel dissimilar metal welding.

Microstructure characteristics of RSW joint: (a) microstructure of cross section of RSW weld; (b) And (c) are the microstructures near the interface of box 1 and box 2 in (a) respectively; (d) (a) IPF image of box 3 in the middle (CGZ is columnar grain area); (e) (a) Vickers hardness chart in the area of box 3 in (a).

Source: Hybrid resistance-laser spot welding of aluminum to steel dissimilar materials: Microstructure and mechanical properties, Materials & Design (2022). DOI: 10.1016/j.matdes.2022.111022