Study On Axial And Circumferential Mechanical Properties Of Extruded 7A04 Alloy Rim

Under the dual requirements of energy and environmental protection,lightweight has become one of the most important means of energy saving and emission reduction.For this reason,the aluminum alloy rim of heavy duty vehicle was developed by extrusion forming,and good results were obtained.In order to improve the microstructure of extruded aluminum alloy wheel rim and further improve its performance,this paper analyzes the axial and circumferential mechanical properties of the wheel rim by means of tensile test,impact test,fatigue test and SEM test.And the reason of anisotropy is analyzed by the microstructure of extruded aluminum alloy wheel rim,which can provide a reference for improving the forming process of aluminum alloy rim.The main conclusions are as follows:(1)The axial and circumferential tensile properties of extruded 7A04 alloy wheels are not very different from each other,and the yield strength and tensile strength are basically the same.The elongated grains and the second phase particles are axially distributed in the surface of the rim,and the circumferential deformation is restricted more.This results in both elongation and cross-sectional shrinkage are lower than the axial,so the axial Plastic toughness is better than the circumferential.(2)The axial and circumferential(the gap on the rim surface)impact properties of wheel are not very different from each other,and this is because the grains and the second phase particles are axially distributed in the surface of the rim,which is more favorable for the expansion of the circumferential crack.However,the grain refinement makes the impact performance difference in both directions decrease,and the axial impact energy is only about 2% higher than the circumferential direction;As the microstructures of extruded rim are stacked in layers along the thickness direction,the sample which has notches on the rim surface consumes more energy during the impact fracture process,and the impact energy is 17.6% higher,and the cross section is also more tortuous.(3)The axial and circumferential fatigue properties of the wheel are different: the circumferential S-N curve is S12.658N=6.639×1036,and the axial S-N curve is S12.987N=7.640×1037.The axial fatigue performance is better than the circumferential direction,and the difference of the fatigue life in the two directions is too small under the condition of high stress,and the difference is big in the low stress state.This is because the grains and the second phase particles are axially distributed in the surface of the rim,which is more favorable for the expansion of the circumferential crack.In the process of axial crack propagation,it is necessary to cut off the fibrous tissue,which has obvious distortion phenomenon,and the crack is not easy to expand.And the axial fatigue crack nucleation particles are larger,so the fatigue life of the micro crack nucleation stage is higher;In addition,the brittle fatigue bands are distributed on the circumferential cleavage step,which has more obvious brittle fracture characteristics.Under the same stress,the circumferential fatigue band spacing is larger than the axial direction,and the smaller the stress is,the larger the difference is,so the circumferential crack propagation rate is faster than the axial direction,and the difference is larger under low stress.