| Magnesium alloys have a great application in automotive, electric manufacture, national defense, aerospace and other fields due to their high specific, high stiffness and machining. ZK60 magnesium alloy is one of the typical high strength magnesium. However, it is easy to form crystallographic texture in process of rolling, which is easy to cause plastic anisotropy, reduce mechanical properties and forming performance. Based on this, the anisotropic of ZK60 magnesium alloys on its deep drawing performance was studied. The research will provide theoretical guidance for the metal plastic forming technology.The initial crystallographic texture of ZK60 magnesium alloy was investigated by using electron backscatter diffraction( EBSD) technology. The Taylor factor value in different loading directions for the sheet was calculated by using EBSD technology. The dependence of the plastic anisotropy of ZK60 magnesium alloy sheet on the Taylor factor was investigated. The plastic anisotropy of ZK60 magnesium alloy sheet was determined by uniaxile tensile tests and the earing behavior was studied by deep drawing tests. The results showed that the plastic strain ratio( r-value) in one direction was dependent on the Taylor factor under load in this direction. The r-value decreased with the Taylor factor value increasing. In addition, the earing direction was consist with the loading direction with the least value of Taylor factor for the sheet. Therefore, the Taylor’s model was quite successful in predicting the plastic anisotropy and its effect on metal’s formability.To provide parameters for deep drawing process and numerical simulation, the mechanical behaviors of deformation at various temperatures, stretch directions and strain rates were investigated by using uniaxial tensile tests. The influences of temperatures, stretch directions and strain rates on flow stress were revealed. The influences of deformation temperatures on strain rate sensitivity and strain hardening were explored. The influences of strain rates on strain hardening were investigated. The results showed that the yield stress and peak stress decreased, the strain rate sensitivity increased and the plastic anisotropy decreased with the increase of temperature. In addition, the strain hardening decreased and strain hardening increased with the rise of temperature.The earing behavior influenced by forming temperature and drawing ratio( DR) in the drawing process of ZK60 magnesium alloy sheet was investigated by using numerical simulation and experimentation. Factors influencing ear formation and evolution in deep drawing test were studied. The results showed that the average earing ratio of the drawn cup increased with the rise of forming temperature, which was related with the planar anisotropy Δr. The average earing ratio increased gradually to a peak value with the rising of drawing ratio, and then decreased with further increase of drawing ratio. The average earing ratio was related with the drawing stages. The average earing ratio was increased with the rise of drawing stages of 20% and 40%. The average earing ratio increased to a peak value and then decreasd with further rising of DR at drawing stages of 60% and 80%. The largest value of the average earing ratio was obtained at DR of 2.17.The thickness strain distribution of ZK60 magnesium alloy drawn cup was studied by wall thickness micrometer gauge. The thickness strain distribution of the drawn cup was investigated at shoulder region, necking region and edge region. The results showed that the thickness strain distribution of the cup along 45° to the rolling direction was higher than those along 0° and 90° directions in the shoulder region because of its high r-value. In addition, it showed that the thickness distribution along 0° was lower than those along 45° and 90° directions at the necking region due to its low r-value.The intensity of ZK60 magnesium alloy drawn cup was studied by microhardness tester. The microhardness distribution of the drawn cup was investigated at shoulder region, necking region and edge region. The results showed that the microhardness distribution of the cup along 45° to the rolling direction was higher than those along 0° and 90° directions in the shoulder region. The microhardness of the cup along 90° to the rolling direction was higher than those along 0° and 45° directions in the necking region which was relate with obtaining the maximum thickness strain increment. The microhardness of the cup along 0° and 90° to the rolling direction was higher than those along 45° direction in the necking region, which was caused by the increase of drawn wall’s thickness and friction. The macrohardness of the drawn cup formed under the temperature of 200℃ was obviously higher than that under 250℃ and 300℃. The drawn cups formed under 250℃ has the lowest microhardness value. |
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