基于控制非平衡冶金反应条件的铝/镁异种合金搅拌摩擦焊技术研究

采用搅拌摩擦焊（FSW）技术焊接异种材料具有较大优势，但对于可能形成金属间化合物（IMC）或低熔点共晶的异种材料，适用的焊接工艺范围窄，尤其是焊接厚板时更为困难。主要原因是：1）焊缝成分处于可析出IMC的区间且焊缝温度较高，析出低熔点共晶或IMC，增加了材料的脆性；2）FSW的热量主要是搅拌头轴肩与材料上表面之间的摩擦，厚板焊接时板材上下温度差很大，容易在焊缝上部出现液相而焊缝下部温度较低而不能焊接的现象。项目针对异种材料FSW出现的困难，选用铝和镁合金作为对象，依据Mg-Al二元相图，研究具有析出IMC和形成低熔点共晶的异种材料FSW技术，阐明焊缝金属成分、非平衡冶金反应在FSW过程中的作用，揭示低熔点共晶对轴肩与被焊材料间摩擦状态变化和焊缝成形的影响及搅拌头形貌、搅拌头与焊接面相对位置等对焊缝成形的影响规律，控制焊缝金属中IMC及低熔共晶体的形成，为异种材料FSW接头提供理理论依据。

The friction stir welding (FSW) has great advantages in welding dissimilar metal materials, but for some kind of materials that may form eutectic materials with low melting point or the intermetallic compound (IMC), the suitable welding parameters range is very narrow, especially when welding thick plates. The main reasons are: 1) the component of the alloy elements in weld may be located in a composition range in which the IMC or the eutectic materials can be precipitated and the weld temperature is rather high, and then the brittleness of the material is increased; 2) the heat during FSW is mainly generated from the friction interface between the tool shoulder and the upper surface of the plate. When welding the thick plate, the temperature between the upper surface and the bottom surface of the plate possesses a big difference. Therefore, when the material at upper surface generates some liquid phase, the material at bottom surface is still at lower temperature and cannot be welded. Aiming at this problem presented in the FSW of dissimilar metal materials, this project selects aluminum alloy and magnesium alloy for the research object. And according to the Mg-Al alloy phase diagram, the FSW of dissimilar materials with the precipitation of IMC and the formation of low melting point eutectic is investigated. The purpose is to clarify the function mechanism of chemical composition in the weld and the non-equilibrium metallurgical reaction in the FSW process, to reveal the affection of the low melting point eutectic on the friction state between the shoulder of the welding tool and the welded material, and the affection of the tool shape, the relative location between the tool center and the welding interface on the weld formation. Finally, the formation of the IMC and low melting eutectic in the weld metal can be controlled, a fundamental basis can be provided for the FSW of dissimilar materials with a good weld formation.