The microstructure and phase constitution near the diffusion bonding interface of Mg/Al dissimilar materials are studied using a scanning electron microscope (SEM), X-ray diffraction (XRD) and transmission electron microscope (TEM). The test results indicated that an obvious diffusion zone was formed near the Mg/Al interface during the vacuum diffusion bonding. The diffusion transition zone near the interface consists of various MgxAly phases. The transition region on the Mg side mainly consists of Mg crystals, and the new phase formed was the Mg3Al2 phase having a face-centred cubic lattice. This is favorable for improving the combined strength of Mg substrate and diffusion transition zone.

Fe3Al intermetallic and 18-8 stainless steel were welded by means of tungsten inert gas (TIG) arc welding. The microstructure performance of the welding zone was analysed using a metalloscope and a scanning electron microscope. The test results indicated that microstructure of the welded metals consists of austenite, proeutectoid ferrite, acicular ferrite, carbide free bainite and lath martensite distributed on the austenitic boundaries as well as grains inside. The microhardness of the fusion zone was lower than that of Fe3Al base metal. The NiAl in the fusion zone was favourable to improve toughness and avoid the welding cracks.

研究了Fe3Al/18-8异种材料扩散焊中工艺参数对界面结合、接头变形状况和剪切强度的影响。采用金相显微镜和扫描电镜（SEM）分析了不同焊接工艺条件下Fe3Al/18-8异种材料扩散焊接头的显微组织特征。结果表明合适的扩散焊工艺参数为：加热温度1020～1040℃，保温时间45～60min，焊接压力12～15MPa.

The distribution of the residual stress in the weld joint of HQ130 grade high strength steel was investigated by means of finite element method (FEM) using ANSYS software. Welding was carried out using gas shielded arc welding with a heat input of 16 kJ/cm. The FEM analysis on the weld joint reveals that there is a stress gradient around the fusion zone of weld joint. The instantaneous residual stress on the weld surface goes up to 800～1000MPa and it is 500～600 MPa, below the weld. The stress gradient near the fusion zone is higher than any other location in the surrounding area. This is attributed as one of the significant reasons for the development of cold cracks at the fusion zone in the high strength steel. In order to avoid such welding cracks, the thermal stress in the weld joint has to be minimized by controlling the weld heat input.

High strength steel; heat-affected zone; M-A constituent; fine structure.