Testing And Analysis On Impact Response Characteristics Of AZ80Magnesium Alloy Loading Wheel

Dynamic testing on components and materials is necessary precondition and theoreticalbasis for R&D of new equipment with high performance, anti impact new materials and highspeed manufacturing technology. Magnesium alloy is the lightest metal structural materials inengineering applications. There are good application prospects in the fields such as aerospace,transportation and weapon equipment. The magnesium alloy loading wheel can enhancemobility and capacity of the armored vehicle by weight reduction and improve theadaptability because of excellent shock absorbing performance. Therefore, it is necessary totest and analyze the dynamic response characteristics of magnesium alloy loading wheels inorder to optimize structure design, improve material to and promote its application.The stress wave propagation characteristics and shock damping of AZ80alloy weretested and analyzed on the freestyle Hopkinson pressure bar. The results show that the stressamplitude increases with bullet speed increasing and decreases obviously with thepropagation distance increasing. While the difference value of the stress amplitude increaseswith the bullets velocity increasing, this is not affected by the length and shape of the bullet.Within the testing range, the stress attenuation coefficient of AZ80alloy was between2.79m-1and5.91m-1and stress amplitude decreases by13～27%. The results of Fouriertransformation of stress-time curve show that the peak of amplitude appears and then declinessharply in the1～4Hz frequency band, which indicates that the optimal frequency of dampingproperties of AZ80alloy wheel is1～4Hz. The AZ80alloy wheel behaves good dampingproperties due to the presence of a large number of weak pinning dislocations according to theG-L dislocation pinning theoretical model.The dynamic mechanical response of AZ80loading wheel (along with the direction ofthe radial direction of plate into0°,45°, and90°), ZK60bar extruded and AZ31castingsamples were tested and analyzed on the split Hopkinson pressure bar. The range of strain rate in this experiment is about800s-1～3000s-1. The dynamic mechanical behaviors werecompared with the quasi-static mechanical behavior. These three kinds of alloy exhibitpositive effect of strain rate. The strain rate sensitivity coefficient of AZ80alloy at0°,45°,and90°directions is0.00669、0.03189and0.03004respectively. With the increasing of strainrate, the maximum stress shows a trend of gradual increasing, which is greatly affected bycompression direction. The maximum strain behaves a trend of suddenly increasing, which isnot affected by the compression direction. For three direction from10-3s-1to3×10-3s-1,themaximum stress increased an average of51.4%and the maximum strain increased an averageof124.6%. On the basis of Johnson-Cook constitutive equation, constitutive model of AZ80alloy at three directions were established.Microstructures and fracture morphology of the samples after testing were analyzed bymeans of the optical microscope and scanning electron microscopy etc. The deformationmechanism, the strain rate sensitivity and fracture mechanism of magnesium alloy under thedynamic impact were discussed. The results show that the deformation mechanism of AZ80alloy under high strain rate is closely related to the loading direction. The plastic deformationmechanism of different directions (90°,45°and0°) is given priority to tensile twin dislocationglide, basal slip and cone slip respectively, accompanied by dynamic recrystallization. Withthe increase of alloy content in magnesium alloy, the area percentages of the twin reducecontinuously, and the role of twin playing in the plastic deformation reduce. Localizeddeformation mechanism of different compression directions is closely related to the loadingdirections. The sample of0°direction formed a deformation localization area consisted oftwin, and the localized deformation of the other two directions is not obvious. Fracturemechanism of AZ80magnesium alloy is the brittle fracture basically. The plasticity improvedwith the increasing of the strain rate.