不同铸型下Al-6.5Mg-0.14Ti-0.12Zr合金的微观组织与力学性能

采用熔模铸造、树脂砂铸造和石膏型铸造等方式成形Al-6.5Mg-0.14Ti-0.12Zr合金,由凝固冷却曲线可知合金凝固温度区间为111.4℃,其中熔模铸造凝固冷速最高,树脂砂铸造次之,石膏型铸造最低。Al-6.5Mg-0.14Ti-0.12Zr合金流动性较佳,可实现不同铸型的完整充型,凝固过程未观察到明显的铸件/铸型界面反应。合金铸态组织主要由α-Al相与Al3Mg2相组成,Al3Mg2相沿晶界均匀分布,与石膏型铸造相比,树脂砂铸造试样中α-Al相平均尺寸由324μm降至132μm;熔模铸造试样抗拉强度、屈服强度、伸长率与硬度(HV)分别为274.7MPa、136MPa、14.9%与60,经400℃×12h固溶后,本体试样抗拉强度、屈服强度、伸长率与硬度(HV)分别增至322.7MPa、144MPa、31.9%与68.3。铸态断口以沿晶断裂为主,可见少量微观韧窝;经固溶处理后断裂方式以韧性断裂为主,韧窝内可见少量的Al3Mg2相、Al3Ti相与Al3Zr相颗粒。

Microstructure and Mechanical Properties of Al-6.5Mg-0.14Ti-0.12Zr Alloy under Different Molds

The solidification cooling curve of Al-6.5 Mg-0.14 Ti-0.12 Zr is distributed according with the Logarithm function,which presents as paste solidification easily due to the temperature interval of 111.4℃.The investment mold obtains the highest cooling rate,which is higher than the resin sand and plaster mold.Absence of casting/mold interface reaction can be observed during the solidification process,and the alloy has excellent filling capability,which can fill completely the different molds.The as-cast microstructure of the alloy is composed ofα-Al phase and Al3Mg2 phase,and the Al3Mg2 phase is distributed uniformly along the grain boundary.The average size ofα-Al phase can be reduced from 324μm to 132μm in resin casting compared with that of ones in plaster mold casting.The average tensile strength,yield strength,elongation and Vickers hardness of investment casting samples reach up to 274.7 MPa、136 MPa、14.9%and 60 HV,respectively.After the solid solution treatment at 400℃for 12 h,the average tensile strength,yield strength,elongation and Vickers hardness of the investment casting samples are increased to 322.7 MPa、144 MPa、31.9%and 68.3 HV,respectively.The as-cast fracture is presented absolutely crystal fracture,and some micro-dimples can be observed.The rupture mode is changed to dimple fracture after the solution treatment,and small Al3Mg2 phase,Al3Ti phase and Al3Zr phase particles are generated in the dimple.