Magnesium alloy, as an ideal lightweight metal structural material, conforms to the development concept of modern lightweighting, energy conservation and emission reduction. Its application prospects in industries such as aerospace, transportation and electronic communication are increasingly valued. The further widespread application of magnesium alloys in various fields also requires the development of processing technology, and welding is an essential key link in the manufacturing of magnesium alloy profiles and the repair of casting defects. The connection problem between magnesium alloys and the same and different metals has continued to receive attention in recent years.
Laser welding has many advantages over other welding methods, such as high power density, simple equipment, high welding efficiency, low residual stress in joints, and narrow heat affected zone. Therefore, it is a highly promising technology for connecting magnesium alloy components. However, the microstructure of magnesium alloy laser welded joints often differs greatly from the base metal, and the strength of the welded joints is generally weaker than that of the base metal. Revealing the correlation between the microstructure and mechanical behavior of laser welded joints is crucial for optimizing the microstructure and welding process of magnesium alloys, and achieving high joint efficiency.
Based on the above issues, Professor Zeng Xiaoqin's team at Shanghai Jiao Tong University conducted research on magnesium alloy laser welding, selecting AZ80 magnesium alloy profiles as the research object. Through a reasonable laser welding process, excellent connection efficiency (>92%) was achieved, further revealing the microstructural evolution of magnesium alloy welded joints and elucidating the strengthening mechanism of magnesium alloy welded joints. The research results were published in the international journal Scientific Reports under the title "On the heterogeneous microstructure and strengthening mechanisms in a laser welding AZ80 magnesium alloy". The first author of the paper is doctoral student Liu Yu, and the corresponding authors are Professor Zeng Xiaoqin, Dr. Wang Jie, and Dr. Zhu Gaoming. The cooperating units also include the Helmholtz Zentrum Hereon Institute in Germany, Lenovo (Beijing) Co., Ltd., the National University of Technology in Korea, and the Deutsches Elektronen Synchrotron (DESY) in Germany.

The welded joint of magnesium alloy AZ80 consists of a fusion zone (FZ), a heat affected zone (HAZ), and a base material (BM). The base material region is composed of equiaxed grains with small grain sizes, exhibiting typical deformation texture characteristics. The grain orientation in the weld zone is random, and the microstructure is similar to that of actual casting, showing the characteristics of central equiaxed grains and edge columnar grains. This is due to the solidification crystallization process during the welding process. In addition, continuous network distribution of Mg17Al12 phase was precipitated in the weld zone during the solidification process. In the AZ80 magnesium alloy laser welded joint, a heat affected zone with a width of about 60 μ m is clearly formed between the weld zone and the base metal. The grain size of the heat affected zone is similar to that of the base material, but its grain boundaries have undergone significant coarsening. In addition, a large amount of small and dispersed Mg17Al12 phase precipitated in the heat affected zone during the welding process.
The magnesium alloy AZ80 welded joint exhibits excellent mechanical properties, with a yield strength of 202 MPa and a welding efficiency of up to 92%. The microstructure analysis using EPMA and EBSD combined with synchrotron radiation X-ray diffraction technology shows that the increase in precipitation phase and dislocation density in the welded joint is the main strengthening mechanism of laser welded magnesium alloy. The combined effect of Orowan strengthening, Heterogeneous Deformation Induced (HDI) strengthening, and strain hardening makes the mechanical properties of AZ80 magnesium alloy welded joints comparable to those of the base metal.