| Research and application on high aluminum zinc-based alloys with various advantages such as high strength, good wear resistance, low density, having low cost raw materials in rich resource and low energy consumption to melt have drawn much attention. However, the application of these alloys is limited because of the poor ductility and toughness (with elongation of 1～3%) due to the casting process used currently. For the research and application of high aluminum zinc-based alloys, domestic and overseas researchers have been laying emphasis on casting field only. However, less fundamental research on wrought high aluminum zinc-based alloys such as component optimization, microstructure and property characterization has been reported. In this paper, based on the high aluminum zinc-based alloy of Zn-26.7%Al-2.5-4.5%Cu-0-0.05%Mg, effect of Mg, Cu elements and their content on the microstructure and mechanical properties of extruded alloy in condition of hot extrusion have been investigated. The study reveals the effect law of Mg, Cu elements and their content, which provides theoretical and technical foundation for developing wrought high aluminum zinc-based alloys and their deep processing technology and widening the application.Extrusion bars of Φ16mm with good quality both in surface and internal have been made for preparing samples used for mechanical properties test and microstructure analysis using a horizontal metal extruding machine. Major extruding process parameters used are as extrusion temperature of 300 ℃, extrusion speed of 1.2～1.5 m min-1, extrusion ratio of 61, preheating the extrusion cylinder and mould at 280～290 ℃, and air cooling applied during extruding. Experiment results show that homogenization treatment processes (with 360℃×12h+300℃ ×3h and 300℃×3h) of ingots has less influence on mechanical properties of as-extruded alloy. It is also shown that, compared with those of casting alloy, the tensile strength and especially the plasticity of as-extruding alloy are increased significantly, due to refiner microstructure and higher relative density formed during hot extruding.Mechanical properties and microstructure of Zn-26.7%Al-2.5%Cu-0-0.05%Mg have been investigated in four states such as-extruded, treated by artificial aging with 95℃×2h, solution treatment followed by air cooling and solution treatment followed by water quenching. It is shown that Mg element and its content have a significant effect on the mechanical properties of the as-extruded alloy such as increasing the tensile strength and hardness while decreasing the plasticity with trace amount of Mg introduced. This effect of Mg element reaches maximum after solution treatment followed by water quenching, while no such effect appears without Mg element added., For the as-extruding alloy containing Mg, the strength and hardness are increased while the plasticity is decreased after artificial aging of 95℃×2h; the strength, hardness and plasticity are all decreased after solution treatment of 320℃×2h followed by air cooling; the tensile strength and hardness are significantly increased while the elongation is decreased with increasing the Mg content after solution treatment of 320℃×2h followed by water quenching. Compared with those of alloy containing no Mg, for an alloy with 0.035%Mg, the tensile strength is increased from 389MPa to 557MPa, with an increase of 43.2%, the brinell hardness is increased from HB107 to HB157, with an increase of 47.6%, but the elongation is decreased from 41% to 20.5% in the condition of natural aging of 15days after water quenching. When Mg content is 0.05%, the tensile strength reaches 617MPa, the brinell hardness reaches HB168, while the elongation is about 0.5～1%, the plasticity mutates and behaves brittle.Study shows that Mg element and its content can affect the eutectoid decomposition microstructure of supersaturated β phase and the dissolution precipitation of supersaturated β phase during aging at room temperature and the morphology of decomposition, thereby the mechanical properties of the alloy can be affected. Mg is an important micro-alloying element for wrought high aluminum zinc-based alloys, in order to improve properties of alloys, the transformation of β phase and decomposition products morphology can be controlled by adding Mg element and employing heat treatment.The effect of various Cu content on microstructure and mechanical properties of alloy Zn-26.7%Al-2.5～4.5%Cu-0.025%Mg in as-extruded state and solution treatment followed by water quenching has been investigated. With the increase of Cu content, the tensile strength and hardness of the alloy are increased, while the elongation is decreased. The amount of ε phase also increases, which is beneficial to improve the wear-resistant property.The fracture microstructure morphology has been analyzed with the aid of SEM, where the fracture mechanism of alloys has been checked. |
PDF Full Text Request