Research On Thermal Simulation Of Aluminum/Magnesium Alloy Cladding Composites During Hot Rolling

The poor corrosion resistance and poor processing ability of magnesium alloy have become the key problems in the industrial application. As a new kind of composite material, aluminum-magnesium cladding composite material can not only improve the corrosion resistance of the magnesium alloy, but also can improve the forming performance of the magnesium alloy, which is a promising material in chemistry and auto industry. However, due to the difference of the two materials, it is very difficult to control the parameters in hot rolling process. In addition, the deformation condition and the thickness of the cladding would not only affect the mechanical properties of the aluminum-magnesium cladding composites, but the stress state and microstructure evolution of the inner magnesium alloy. The thesis is aim at studying the hot compression test at different deformation temperature and different strain rate of Al-Mg cladding material which is composed of the annealed AA5052 alloy and annealed AZ31 alloy, using the thermal mechanical simulation. After getting the true stress of different deformation condition, then we study how the strain rate, deformation temperature and cladding thickness affect AA5052/AZ31 cladding material's flow stress.The main results obtained are as follows: peak flow stress and peak strain of the Al/Mg cladding composite are gradually increased with increasing the strain rate; the peak stress and peak strain of Al/Mg cladding composite are gradually reduced with increasing the deformation temperature; the peak stress decreases with the decrease of the thickness of the cladding, but the peak strain increases gradually; while the cladding thickness is small, the stress-strain curves would appear stress overshoot, the peak of stress overshoot decreases gradually with the increase of the cladding thickness. Meanwhile, the constitutive equation of AZ31 magnesium alloy inside the cladding composite was set up in the constraint state of different cladding thickness by using the Johnson-Cook model, drawing some conclusions: with the decrease of cladding thickness, the sensitivity coefficient “C” of strain rate and sensitivity coefficient “m” of deformation temperature for AZ31 inner core material decreases gradually.The microstructure of AZ31 magnesium alloy inside the cladding material was observed and analyzed by optical microscopy(OM). The microstructure indicates that the center of the specimen position presents a very fine and equiaxed grain morphology and the head face presents a relatively coarse grain state, while the interface of aluminum and magnesium presents a obvious rheological microstructure. The dynamic recrystallization grain size under large strain rate is smaller than that of the small strain rate. Along with the cladding thickness decreases, the grains of the AZ31 magnesium alloy microstructure recrystallize more fully and the flow stress decreases gradually before the cladding thickness is reduced to 1 mm(the size of AZ31 core is 8 mm in diameter), but the flow stress of the inner AZ31 alloy goes up suddenly during the cladding thickness is reduced to the minimum. The hardening effect is dominant at low temperature, but the dynamic softening action takes the leading role with the increase of deformation temperature on account of dynamic recrystallization.