Effect Of Iron Phase On High Temperature Mechanical Properties Of ZL114A Al-Si Alloy

ZL1114A A1-Si alloy are widely used in such industrial field as aerospace engineering and automotive manufacture. Iron is the most common impurity in Al-Si alloys, and the fragile iron phase deteriorate the normal use of alloy. The transformation method that between iron phases is used to reduce the harmful effect to alloys. Now, iron phase morphologies change methods in the alloy have not reached a consensus between domestic and foreign scholars. The iron is a common in the alloy, the effect of it on the high temperature mechanics properties of alloy have not been system research. In the thesis, addition of manganese and strontium were made to improve the morphology of iron phase in A1-Si alloys; The room temperature and high temperature tensile properties were studies by using WDW-20micro-control electronic universal test machine and DH3818static strain indicator; The high temperature fatigue properties were studies by using HT-9710-10fatigue testing machine.The results showed that addition of manganese could effective change the needle-like iron phase into fishbone-leke or Chinese script iron phase. The change was stable when the iron content in alloy was1.0%and the manganese content was0.5%. Addition of strontium couldn't change the β-AlFeSi phase into α-AlFeSi phase, it could only make the β-AlFeSi phase bend, fracture and decomposition, but could do a goog modification to silicon phase. Addition of manganese was the most effective methods to make the iron phase changed. The optimized addition amount is ω(Fe)/ω(Mn)=2:1and ω(Fe)=1.0%.The needle-like β-AlFeSi phase can improve the room temperature and200℃yield strength and ultimate tensile strength of alloys, but reduce the elongation of alloys. The fishbone-like α-AlFeSi phase can improve the elongation and room temperature yield strength of alloys. The fracture surface microstructures were observed by using OM and it was found that the crack was wear crystal fracture in room temperature tensile and transgranular fracture in high temperature tensile. The fractographs were observes by using SEM and it found that the fracture of sample with needle-like iron phase is the brittle fracture and the fracture of sample with fishbone-like iron phase was typical ductile features in the room temperature and high temperature tensile test.The fatigue strength of the sample with needle-like iron phase is57.5MPa under the106times fatigue cycle and higher than them of ZL114A sample and sample with Chinese script iron phase; The theoretical model for fatigue life at200℃was developed by combining the high temperature ultimate tensile strength of three groups of samples; The fractograph was observed by using the OM and found that the crack in the sample with needle-like iron phase propagated along the iron phase, the crack in the sample with Chinese script iron phase cut the phase directly and the structure of iron phase far away the surface had also fracture; Fracture surface was observed by SEM and it was found that the fatigue crack is always initiated from the cast defect which is located at the edge of sample, The fracture of sample is resulted from the subsequent crack propagation form the edge to the inner area of the sample.