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利用挤压铸造技术,在不同比压下制备Al-6Zn-2.5Mg-1.8Cu合金坯料,然后对性能最好的挤压铸造坯料进行固态热挤压。结果表明:比压从0增加到250 MPa时,树枝晶变得细小而圆整。由于外加压力增加了合金元素的固溶度,因此,MgZn_2相数量减少。当比压从250MPa增加到350 MPa时,合金的晶粒尺寸变大。固态热挤压后,α(Al)树枝晶被明显细化,并且MgZn_2相均匀弥散地分布在合金的显微组织中。固态热挤压后,合金的极限抗拉强度为605.67 MPa,伸长率为8.1%。与金属型铸造合金相比,抗拉强度增加了32.22%,伸长率增加了15.71%。金属型铸造和挤压铸造的断裂方式分别为沿晶断裂和准解理断裂。然而,挤压铸造成形后固态热挤压工艺的合金断裂方式为韧窝断裂。细晶强化作用是合金抗拉强度和伸长率提高的主要原因。
Al-6Zn-2.5Mg-1.8Cu alloy billets were prepared at different specific pressures by squeeze casting technology, and then the best performance of the extrusion cast billets was solid-state hot-extruded. The results show that when the specific pressure is increased from 0 to 250 MPa, the dendrite becomes fine and round. As the applied pressure increases the solid solubility of alloying elements, the amount of MgZn2 phase decreases. When the specific pressure is increased from 250 MPa to 350 MPa, the grain size of the alloy becomes larger. After solid state extrusion, the α (Al) dendrites were obviously refined, and the MgZn_2 phases were uniformly dispersed in the microstructure of the alloy. After the solid state hot extrusion, the ultimate tensile strength of the alloy is 605.67 MPa and the elongation is 8.1%. Compared with the metal casting alloy, the tensile strength increased by 32.22%, the elongation increased by 15.71%. Metal-type casting and squeeze casting fracture mode were intergranular fracture and quasi-cleavage fracture. However, the fracture mode of the alloy after extrusion casting and forming is the dimple fracture. Fine grain strengthening is the main reason for the increase of tensile strength and elongation of the alloy.