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采用反向挤压技术将AZ31镁合金和纯铝材料在不同温度下挤压形成包覆棒材。挤压过程中纯铝包覆在镁合金外侧,镁铝间形成冶金结合界面,实现了镁铝双金属的复合。挤压完成后使用光学显微镜(OM)、扫描电子显微镜(SEM)及能谱(EDS)分析技术对镁铝包覆挤压合金进行了组织及力学性能分析,重点研究了铝镁合金结合界面处化学成分过渡及相结构的演化与分布,同时采用显微硬度计测试了镁铝结合界面的显微硬度。结果表明,通过反向热挤压工艺可以得到表面光洁、无明显缺陷的铝镁合金包覆挤压制品。在高温高压条件下,镁铝复合金属在界面结合区发生了元素扩散,铝镁合金浓度出现明显的梯度变化,进而在结合界面上发生冶金反应,形成约350μm厚的金属间化合物层,物相分析表明在靠近镁合金基体一侧生成富镁相Al12Mg17,靠近纯铝一侧生成富铝相Al3Mg2,主要为脆性相生成。沿包覆棒材横截面直径方向从边部到芯部进行显微硬度测试,结果表明,该合金包覆型材具有明显的力学不均匀性,在铝镁结合界面处的硬度高于两侧基体材料,其峰值硬度可达HV 200以上,包覆型材在结合界面的组织差异和强度、硬度失配导致结合界面的力学性能急剧弱化,容易产生开裂。
Using reverse extrusion technology, AZ31 magnesium alloy and pure aluminum material are extruded at different temperatures to form coated rods. In the extrusion process, pure aluminum is coated on the outside of the magnesium alloy, and the metallurgical bonding interface is formed between the magnesium and aluminum to realize the composite of magnesium-aluminum bimetal. After extrusion, the microstructures and mechanical properties of the Mg-Al-clad extruded alloy were analyzed by optical microscope (OM), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) Chemical composition transition and the evolution and distribution of phase structure, and at the same time the microhardness of magnesium-aluminum interface was tested by microhardness tester. The results show that aluminum-magnesium alloy coated extrusion products with smooth surface and no obvious defects can be obtained by reverse hot extrusion process. Under the conditions of high temperature and high pressure, the elemental diffusion of Mg-Al composite metal occurs in the interface bonding zone, and the gradient of Al-Mg alloy changes obviously, and then the metallurgical reaction occurs at the bonding interface to form an intermetallic compound layer with a thickness of about 350 μm. The analysis shows that Al12Mg17, a phase rich in magnesium, is formed close to the matrix side of the magnesium alloy, and Al3Mg2, which is an Al-rich phase near the side of pure aluminum, is mainly formed by the brittle phase. The results of microhardness testing from the edge to the core along the diameter of the cross-section of the clad bar showed that the cladded section had obvious mechanical inhomogeneity and the hardness at the interface of aluminum-magnesium bonding was higher than that of the two sides Materials, the peak hardness of up to HV 200 above, the profile and strength of the coated profiles in the bonding interface, the hardness mismatch led to a sharp weakening of the mechanical properties of the bonding interface, prone to cracking.