Study On Fatigue Behavior Of AZ80 Magnesium Alloy Wheel

As the main component of wheel tracked vehicle,loading wheels play a decisive role in safety,comfortable,stability of track-laying vehicle,so it is the superior choice to reduce the weight of the loading wheel in lightweight design of weapon system,and magnesium alloy turns into the first choice to produce the loading wheel because of its superior performance.The loading wheels suffer from a variety of alternating loads in the process of driving,which easily causing fatigue failure.It is essential for boosting the widely application of the loading wheel to promote the fatigue performance and increase fatigue life of the loading wheel,and the forming process directly affects the performance of road wheel,therefore aiming at the radial-reverse composite extrusion process,the fatigue properties of the AZ80 magnesium alloy loading wheel by the technology was researched and analysed systematically,and there is a notable practical significance to improve the forming process,and promote the application of magnesium alloy loading wheel.In this paper,firstly the technological process of forming the loading wheels is simply introduced,which is the procedure of the radial-reverse composite extrusion.Secondly intercepting the sample from the loading wheel straight wall part and bottom part along the extrusion direction,the microstructure was investigated by the ZEISS microscope and the tensile tests were performed using the INSTRON 3382 universal testing machine.Then intercepting the sample from the loading wheel wall part along the extrusion direction,the high cycle fatigue experiment and the crack growth rate test were performed by the INSTRON8801 fatigue testing machine,measuring the fatigue strength and fracture toughness,and the fatigue fracture morphology was analyzed by using SU5000 scanning electron microscope.The grain size on the wall part and the bottom part of the AZ80 magnesium alloy loading wheel is small and equiaxed,the second phase on the straight wall part is precipitated by point,rod and lamellar,while the second phase on the bottom part is precipitated by graininess.The tensile strength of the wall specimen is 301 Mpa,the elongation is 9.8%,and the bottom sample is 285 Mpa,the elongation is 9.3%,that is,the strength of the straight wall is large and the plasticity is good,the difference percentages were 5.3% and 5.1%,respectively.It is shown that the loading wheel formed by the radial-reverse composite extrusion could realize the uniformity of the structure and properties.The results of the high cycle fatigue test show that the value of fatigue strength is about 102 Mpa whether obtaining from the S-N curve or being calculated by the formula,comparing with Zeng Rongchang?s study,the value of fatigue strength is increased about 10 Mpa.It indicate notably that the fatigue strength of the loading wheel could be improved y the radialreverse composite extrusion technology.The fracture morphology shows that the crack is initiated from the sample surface,there are fatigue striations,secondary crack,cleavage step and feather pattern in the crack extensive zone,and the fracture zone includes secondary crack,dimple,cleavage and quasi cleavage step,tearing edge.The results of the fatigue crack propagation experiment show that the value of the fracture toughness is tested by the COD.It could be obtained from the da/dN-?K curve that the capacity is reduced to resist the crack propagation through overaging treatment.After the fracture morphology being checked,the fatigue crack initiate from different post,the crack source of the overaging treatment sample presents a smooth and flat profile in the prefabricated crack area,and the crack initiation of the peak aging treatment samples shows quasi cleavage like stream.Comparing with the peak aging treatment specimens,the interval of the fatigue strip propagation trace in the crack extensive zone for the overaging treatment samples is greater,and the dimple is less and more shallow in the fracture area of the overaging treatment specimens.It indicates that the fatigue life of the loading wheel is reduced through overaging treatment.