镁作为一种重要的轻金属工程材料，因其优异的性能在航天领域、轨道交通领域以及军工领域有着广泛的关注。TIG焊是镁合金常用的一种焊接方法，但TIG熔焊接头焊接质量差，接头的力学性能普遍降低，难以满足焊接工程结构的要求。本文以AZ31B镁合金TIG焊接头为研究对象，分别对焊接接头进行固溶处理、固溶与时效处理试验，研究了热处理方法及工艺参数对焊接接头的微观组织、力学性能和腐蚀性能的影响规律。得到了以下主要结论： （1）未热处理的接头焊缝以细小的等轴晶分布，由α-Mg基体和沿晶界呈断续网状分布的Mg17Al12相构成。热影响区沿晶界分布少量短条状的Mg17Al12相，晶粒粗大。焊缝产生强化硬度最高，而热影响区发生软化硬度最低。 （2）固溶处理后接头组织中Mg17Al12相向α-Mg基体中发生不同程度溶解，420℃×8h固溶处理的接头组织中的第二相的溶解量最多，晶粒尺寸最均匀。固溶态的接头和未热处理的接头硬度分布趋势相同，均呈阶梯状分布。随着固溶时间的延长，接头的拉伸强度呈先上升后下降的变化规律，420℃×8h的接头抗拉强度最高达201MPa，比未热处理的接头提高了23%，接头呈韧性断裂为主的韧脆混合型断裂形貌。 （3）时效温度和时效时间影响接头组织中Mg17Al12强化相的分布形态，随着时效温度和时效时间的增加，接头焊缝区Mg17Al12相的分布形态由颗粒状变为团聚状分布。接头焊缝区、热影响区的显微硬度和接头拉伸强度均呈先增加后减小的变化趋势，200×8h时接头各区域的硬度均达到最大值；接头的抗拉强度达到最大值230MPa，比固溶420℃×8h的接头提高了15%。随着时效时间的延长，接头具有从韧性断裂向脆性断裂转变的特征。 （4）不同热处理状态的接头在3.5%NaCl中浸泡后，镁合金母材耐蚀性最佳，其次是焊缝，热影响区的耐蚀性最差。热处理工艺对AZ31B镁合金焊接接头的耐蚀性具有较大影响。420℃×8h固溶处理的接头耐蚀性最好，200℃×12h时效处理的接头耐蚀性最差。与未热处理的焊接接头焊缝区相比，420℃×8h固溶处理的焊接接头自腐蚀电流密度为2.82×10-6 A/cm2，降低了近一倍，腐蚀电位升高；200℃×12h时效处理的焊接接头的自腐蚀电流密度增加了2.2×10-6 A/cm2，腐蚀电位降低。

Magnesium as an important light metal engineering material, has attracted extensive attention in aerospace, rail transit and military industries due to its excellent performance.TIG welding is a common welding method for magnesium alloys, but the welding quality of TIG welding joints is poor, the mechanical properties of the joints are generally low, Which is difficult to meet the requirements of welding engineering structure.This article takes AZ31B magnesium alloy TIG welded joint as the research object, solid solution treatment,solid solution and aging treatment test are performed respectively. The influence of heat treatment method and process parameters on microstructure, mechanical properties and corrosion performance of the welded joint are studied. The following main conclusions have been obtained: (1)The weld zone of unheated weld joints are distributed with fine equiaxed grain, consisting of α-Mg matrix and Mg17Al12 phases which distributed discontinuously along grain boundaries. The heat-affected zone distributes a small number of short strip Mg17Al12 phases along the grain boundaries, and the grains are coarse.The weld zone produced the highest hardness, while the heat affected zone has the lowest hardness. (2) After solution treatment, the Mg17Al12 phase in the joint dissolves into α-Mg matrix with different degree. At solution condition of 400℃×8h,the second phase in the joint dissolves most,and the grain size is the most uniform. The solid solution joints and unheated joints have the same hardness distribution trend, both show a stepped distribution. With the increase of the solution time, the tensile strength of the joints increases first and then decreases. At solution condition of 420°C×8h ,the tensile strength of the joints reaches 201MPa, which is 23% higher than unheated joints. The joints mainly show ductile fractures with tough-brittle mixed fracture morphology. (3)Aging temperature and aging time affect the distribution of the Mg17Al12 strengthening phase in the joint. With the increase of aging temperature and aging time, the distribution of the Mg17Al12 phase in the weld zone changes from granular to aggragated. The microhardness of weld zone , heat-affected zone and the tensile strength of the joints both showed the trend of increases first and then decreases. At aging condition of 200×8h, the hardness of each area of the joint reached the maximum; and the tensile strength of the joints reached maximum of 230MPa, which is 15% higher than solution condition with 420°C×8h.With the extension of aging time, the joint has a characteristic of transition from ductile fracture to brittle fracture. (4)After different heat treated conditions joints soaked in 3.5% NaCl, the corrosion resistance of magnesium alloy base metal is the best, the weld zone is followed, and the corrosion resistance of the heat affected zone was the worst. The heat treatment process has a great influence on the corrosion resistance of AZ31B magnesium alloy welded joints. The corrosion resistance of the joint performance the best at the solution condition of 400°C×8h. The corrosion resistance of the joint performance the worst at the aging condition of 200°C×12h. Compared with weld zone of unheated joint, the self-corrosion current density of the joint treated with solution of 420°C×8h was 2.82×10-6 A/cm2, which is reduced into one times compared with unheated joint, and the corrosion potential was increased; The self-corrosion current density of the joint treated with aging condition of 200°C×12h increased by 2.2×10-6 A/cm2, and the corrosion potential decreased.