摘要
Al-6Zn-2.5Mg-1.8Cu alloy ingots were prepared by squeeze casting under different specific pressures,and the fresh ingot with best mechanical properties was solid hot extruded.With the increase of the specific pressure from 0 to 250 MPa,the dendrites became round and small.Because the applied pressure increased the solid solubility of alloying elements,the number of MgZn2 phases decreased.When the specific pressure increased from 250 MPa to 350 MPa,the grain size increased.After solid hot extrusion,the a（Al） grains were refined obviously and the MgZn2 phases were uniformly dispersed in the microstructure.After solid hot extrusion,the ultimate tensile strength was 605.67 MPa and the elongation was 8.1%,which were improved about 32.22%and15.71%,respectively,compared with those of the metal mold casting alloy.The fracture modes of the billet prepared by the metal mold casting and by squeeze casting were intergranular and quasi-cleavage fractures,respectively,whereas,that of the solid hot extrusion was mainly dimple fracture.The refined crystalline strengthening was the main reason to improve the strength and elongation of alloy.
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。
基金
Project(50971092)supported by the National Natural Science of Foundation of China
Project(201202166)supported by the Natural Science Foundation of Education Department of Liaoning Province,China
