Study On Uniformity Of Microstructures And Mechanical Properties Of Wide AZ31 Magnesium Alloy Plate

Wide magnesium alloy plates have broad application prospects in transportation,aerospace and other fields.Magnesium alloy ingot hot rolling is the main method to produce wide magnesium alloy plates.However,due to the HCP crystal structure characteristics and its poor plasticity,magnesium alloy can only be processed by hot deformation.And its low heat capacity and low thermal conductivity can easily lead to uneven temperature in the process of plastic deformation,which leads to uneven deformation.For the above reasons,the uniformity of microstructures and mechanical properties of wide magnesium alloy plates require more stringent process control during rolling deformtion.However,there are a lack of researches on the uniformity of microstructures and mechanical properties of wide magnesium alloy plates about rolling technology.Therefore,the research on the uniformity of microstructures and mechanical properties of wide magnesium alloy plates has important guiding significance for the optimization and control of rolling process.This paper takes the 1500mm AZ31 magnesium alloy plates produced by ingot-hot rolling method as the research objects.The variation of the temperature,stress and strain of the wide magnesium plates with thickness ranging from 3mm to 30mm during the hot rolling process were studied by numerical simulations.The microstructures,mechanical properties and texture uniformity of four typical thickness wide plates were investigated through process tests.On the above basis,the relationship between the microstructures and mechanical properties of the wide plates is analyzed.The main conclusions are as follows:(1)Numerical simulation results show that the temperature distribution of plates in thickness and width directions are uneven during rolling.The overall performance is that the surface temperature is lower than the center layer,and the edge temperature is lower than the middle.With the increase of rolling passes,the temperature difference between the surface layer and the central layer of the rolling plate decreases to 20?.The temperature difference between the edge and the middle part of the rolling plate increases gradually,and the biggest temperature difference reaches 30?.The equivalent stress in the rolling deformation zone gradually increases from the middle to the edge in the width direction,and the equivalent stress in the middle is about 15MPa smaller than the edge.The equivalent stress distribution is uneven.With the progress of rolling,the strain difference between the edge and the middle increased from 0.05mm/mm to 1mm/mm.(2)The microstructures and mechanical properties of wide magnesium plates with larger thickness(13mm and 18mm)are uniform in both width and thickness directions.Microstructures are incompletely recrystallized structures.The uniformity of average grain size and tensile strength of the 18mm thickness plate are better in the thickness direction than that in the width direction.The biggest difference of grain size and tensile strength in thickness direction is 7 ?m and 3 5MPa respectively.The biggest difference of grain size and tensile strength in width direction is 12?m and 40MPa respectively.The uniformity of average grain size and tensile strength of the 13mm thickness plate are significantly improved.And the microstructures uniformity in width direction is better than that in thickness direction.The biggest difference of tensile strength in both width and thickness directions are within 10MPa.(3)The difference in average grain size of wide magnesium plates with smaller thickness(3mm and 6mm)is very small.There are more shear bands and twins at the edge in width direction.And grain size dispersion is also significantly larger than that in the middle.The uniformity of the tensile strength of 6mm thickness plate is poor in width direction,and the difference in elongation is small.The uniformity of the tensile strength of 3mm thickness plate is better in width direction,and the difference in elongation is lager.(4)Based on the existing models for the relationship between microhardness and tensile properties,a mathematical relationship between tensile strength and yield strength was established by eliminating the intermediate variable of microhardness.Combined with Hall-Petch relationship and the relationship between tensile properties and average grain size was obtained.