Effect Of Bending Rolling Process On The Properties Of AZ31 Magnesium Alloy Sheet

The magnesium alloy has the advantages of small density, high specific strength and specific rigidity, good shock absorption, good thermal conductivity and so on,it is called "the green environmental protection structure material in twenty-first Century". It has very important application value and broad application prospects in many fields such as aerospace, automotive, electronics, electrical appliances, communication and so on. But because of magnesium alloy with hexagonal close-packed crystal structure, it has poorly forming performing at room temperature and is easy to produce strong basal texture especially in the rolling forming process,which is key problems of caused magnesium alloy rolling sheet material breakage and limits the important bottleneck of large-scale use. In order to improve the forming ability of the magnesium alloy at room temperature, it is necessary to study and develop a new type of rolling process to improve its room temperature plasticity.In this paper, the commercial cast-rolling state AZ31 magnesium alloy is used as the research object. The mechanical performance, microstructure and texture change of magnesium alloy sheet were studied under different bending rolling process conditions. The effects of bending rolling passes, material preheating temperature, bending mode and rolling speed ratio on the mechanical properties, microstructure and texture changes were analyzed. Results show:1) The rolling passes and the preheating temperature have a significant effect on the performance of the magnesium alloy sheet at room temperature. The deformation energy of the material is accumulated in the bending rolling times. As the deformationenergy can directly affect the degree of recrystallization of AZ31 magnesium alloy, and futher prove alternating bending rolling process which has influence on its macro-mechanical performance.The results show that the central part of the 10 times is still the original organization, and is not completely recrystallization.Complete dynamic recrystallization occurred in 12 times. After 14 times of recrystallization, the grains are deformed, and appeared the deformation structure. As the microstructure impact the material macro performance, the elongation of the 12 passes bending rolling test is the largest, and the strength is greater than 14 times. That is to say,12 times is the best way to bend. Secondly, the preheating temperature of magnesium alloy sheet will also affect the microstructure and mechanical properties of the material, but the effect of preheating temperature on the micro structure and properties of the material is obviously less than that of the rolling passes. Only the bending rolling passes is 12 or above and the material preheating temperature is 350? or 400?,the elongation rate can be increased obviously. In the 10 times, the material preheating temperature has no obvious effect on the room temperature properties of the material.2) The temperature and the bending rolling passes of the plate obviously influence the AZ31 room temperature performance parameters. The results of bending and horizontal rolling experiment show that,the plasticity and the strength of the sheet metal obtained at 350? and 400? were higher than 300? at the same bending rolling times. But the effect of the rolling times on the room temperature properties of AZ31 is higher than that of the preheating temperature of the plate. Preheating temperature of 400?, the 12 times of the rolling pass is the maximum plasticity and strength of the sheet metal, it has little difference with 350?. The 12 times is the best rolling pass and the best preheating temperature is at 350? and 400?.3) The way of bending rolling has influence on the strength and elongation of AZ31 magnesium alloy. Studies have shown that alternating bending rolling texture is {0001} basal texture, but bending and horizongtal rolling process of texture is{0001}<11 20> sheet texture. The basal texture of alternating bending rolling appeared RD and TD direction deflection rarely, but bending and horizontal rolling process of the texture is relatively RD and TD direction deflection of 20° and 8°, so texture is weakened. Therefore, the strength and elongation of AZ31 sheet obtained by bending and horizontal rolling process are significantly higher than that of alternating bending rolling process in the same rolling passes and preheating temperature. The preheating temperature of 350?,12 times bending and horizontal rolling process of AZ31 sheet obtained yield strength and tensile strength that was 180MPa and 284MPa respectively and its extending rate was 20.6%,and at the same rolling condition,alternating bending rolling process obtained yield strength and tensile strength that was 149MPa and 279MPa respectively, and its extension rate is only 12.9%.4) The rolling speed ratio of roll can affect the strength and elongation of magnesium alloy sheet. With the increase of the speed of the big roller, the total elongation rate changes of the material is decreased, but the intensity changes is rule less. The research shows that when the rolling speed ratio is 1.0:1.2 and 1, the texture is {0001}<1120> plate texture, and the texture of the former is relative to RD and TD direction deflection of 20° and 8°, so the texture is weakened. When the velocity of the large roller continued to increase, the texture of the ratio 1.0:0.8 is {1010}<1120>plate texturet. The influence of the rolling speed ratio on the elongation of the material is less than that of the material forming way. In the 400? preheating temperature bending and horizontal rolling, the rolling speed ratio of AZ31 magnesium alloy material is less affected. And In the 350? preheating temperature bending and horizontal rolling, the rolling speed ratio of the AZ31 magnesium alloy material is more affected.