镁合金的电弧熔敷与搅拌摩擦处理复合成形再制造方法与机理研究

Aiming at the problem of remanufacturing of worn-out magnesium alloy parts, a new hybrid forming method of welding arc deposition and friction stir processing is put forward, on the basis of welding arc deposition additive and milling subtractive hybrid rapid forming technology. The cold metal transfer arc welding technology will be applied to realize a low deformation deposition process of magnesium alloy. The droplet transfer and forming mechanism of magnesium alloy would be studied in the cold metal transfer arc welding deposition process. The numerical analysis model of thermal stress and strain in the forming process will be built. The formation mechanism and distribution of defects, such as coarse microstructure, porosity and residual stress, will be analyzed. The friction stir processing will be exerted on the cladding layers to enhance its property and dimensional accuracy in a integrative way. The dynamic recrystallization process will be studied in the friction stir processing of the non smooth thin cladding layers. The influence mechanism of friction stir processing on the performance and dimensional accuracy of arc cladding layer will be clarified. The mechanism of reducing the residual stress produced by the plastic deformation of the material caused by friction stir processing will be revealed. The numerical model of the mechanical response of the stirring head will be established. The low stress friction stir processing will be realized through adjusting of the acting force on the stirring head. This study can provide a scientific basis for the development of a new remanufacturing technology worn-out magnesium alloy parts.

针对废旧镁合金零件的再制造难题，在电弧熔敷增材/铣削减材复合快速成形技术基础上，提出一种电弧熔敷与搅拌摩擦处理复合成形再制造方法。采用冷金属过渡电弧焊熔敷技术实现镁合金的低形变熔敷成形：研究镁合金冷金属过渡电弧焊熔敷过程中熔滴过渡及成形机理，建立熔敷成形过程热应力应变数值分析模型，分析熔敷成形层中粗大组织、气孔、残余应力等缺陷的产生机理及分布形态。运用搅拌摩擦处理技术实现熔敷成形层的性能与尺寸精度一体化处理：研究非平整面薄层状态下搅拌摩擦处理中金属组织的动态再结晶过程，阐明搅拌摩擦处理对电弧熔敷成形层性能与尺寸精度的影响机理，揭示搅拌摩擦引发的材料塑性变形消减熔敷成形过程产生的残余应力的机理；建立搅拌头力学响应数值分析模型，通过对搅拌头受力的调控实现低应力搅拌摩擦处理。本研究可为发展一种新的废旧镁合金零件再制造技术提供相关科学依据。

针对武器装备、轨道交通等领域中大尺寸镁合金零部件电弧熔敷修复时存在的残余应力过大、成形层表面及内部易产生沟槽及孔洞等缺陷，本项目提出并研究了一种冷金属过渡焊熔敷成形+搅拌摩擦后处理的镁合金零件再制造技术及其机理。研究了镁合金的冷金属过渡电弧熔敷成形机理及成形规律，采用摆动焊方法实现了大面积镁合金熔敷成形，解决了镁合金搭接成形时沟槽缺陷。以AZ31镁合金为研究对象，分析了镁合金的冷金属过渡电弧焊熔敷成形性能及缺陷。与基体材料相比，冷金属过渡电弧熔敷成形层组织细小，但在热影响区产生了晶粒长大现象。由于镁合金的热导率较大，导致熔池凝固速度过快，在熔敷成形焊道之间容易产生孔洞缺陷。开展了镁合金熔敷成形层搅拌摩擦加工工艺研究，设计出适用于镁合金电弧熔敷成形层搅拌摩擦加工的搅拌头，实现了非平整表面状态下的搅拌摩擦加工。研究了搅拌摩擦加工对镁合金电弧熔敷成形层几何形貌、显微组织、力学性能、残余应力及耐腐蚀性能的影响。在搅拌摩擦加工过程产生的热与机械搅拌双重作用下产生金属塑性流动，电弧熔敷成形层表面沟槽以及内部孔洞缺陷消失。搅拌摩擦加工细化了AZ31镁合金电弧熔敷成形层及热影响区的显微组织，高温塑性提高了44%，但降低了抗拉强度，耐腐蚀性能得到提高；熔敷层表面产生了残余压应力，测量的最大残余压应力为-52MPa。