Study On Strengthen And Toughening Mechanism Of Al-Cu Alloys Casts Formed By Squeeze Casting

In the field of equip and manufacture industry, for the sake of economizing material and reducing energy sources depletion, lightening the weight of components is the target that the people pursue over a long period of time, is also one of development trend of modern manufacturing technique. The lightweighting can be realized by adopting light metal or higher strength material. The stengthen and toughening of Al alloy colligate the way of lightweighting. In the experiment, via the squeeze casting to form Al-Cu alloy mainshaft retainer of high speed machine tool, the effects on the casts mechanical properties and microstructure of squeeze casting process parameter, the content of elements and heat treatment are investigated.The results of experiments show that the influence order of processing parameter on tensile strength is the intensity of pressure, the mold temperatures the pouring temperature, the time of pressure holding, and the influence order of that on extensibility of the casts is the intensity of pressure, the time of pressure holdings the pouring temperature, the mold temperature. The values of optimal process parameters are that the intensity of pressure is 140MPa, the time of pressure holding is 24s, the pouring temperature is 775°C , and the pouring temperature is 210 °C. The intensity of pressure is the most markable factor that influence the casts mechanical properties and microstructure. When its value exceeds 40MPa, the disfigurement such as shrinkage porosity can be effectively reduced . when its value exceeds 120MPa, the pressure obviously influence the crystal performances of liquid metal also, and compact homogeneous exiguous equiaxial crystal can be obtained. Pressure can also increase the solubility of Cu in a -Al. distinguished from the Cu content which have the optimal effect on cast strength is 5% with the chill casting, the Cu content that have the optimum effect on cast is 8% in the squeeze casting, furthermore, its strength effect is much better. The vacancy consistency of casts is raised in the squeeze casting which makes speed the diffuse velocity of atom and heat treatment process. The solution treatment of casts almost accomplished under conditions of keeping thecasts for 4 hours with 525℃⁵30℃. Adding the time of solution treatment process, the casts mechanical properties can be little enhanced, which is most optimal when the time of solution treatment is 15 hours. The natural aging process can easily happen, and the Cu atom can separate out to form GP region and 6 " phrase which have the very good effect on strength of casts and can be stably existed under the natural environment. Casts mechanical properties is so much better when casts are under the condition of natural aging than that of the casts which are under the condition of T6.The mechanical properties of casts acquired under the conditions of optimal process parameters is satisfying. The mechanical properties of as-casting casts which Cu content is 2%, 5%, 8% are σ_b=211.9MPa, δ₅=16.0%; σ_b =234.2MPa,δ₅=8.1%; σ_b=255.0MPa,δ₅=2.2% respectively. The mechanical properties of casts being treated by the proper heat treatment process are σ_b=287.6MPa,δ₅=20.3%; σ_b=389.6MPa,δ₅=10.8%; σ₅=405.3MPa,δ₅=8.3% respectively. The satisfactory retainer of high speed machine tool was obtained.