Effect Of Mo Alloying On Microstructure And Properties Of Al-Mg And Al-Mg-Si Alloys

Aluminum alloy material has the characteristics of light and high strength.Compared to steel with the same span,aluminum alloy structures can reduce self-weight by 20%-30%.Because of its strong plasticity,beautiful appearance,good surface performance,good economic benefits,and being able to better meet the structural needs of complex architectural modeling,it is widely used in buildings,Bridges and other long-span space structural buildings.But the fire resistance of aluminum alloy structure is poor,and the structural performance will be seriously degraded in a short time,so the fire protection design is particularly important.At present,the development of refractory aluminum alloy is still a relatively new direction at home and abroad,and theoretical research is extremely scarce.In this study,Al-Mg alloy with Mo element content of 0%,0.08%,0.17%,0.37%,0.53%and 0.86%and Al-Mg-Si alloy with Mo element content of 0%,0.11%,0.27%,0.36%,0.39%and 0.70%were selected as test objects.With metallographic microscope,scanning electron microscope,X-ray diffractometer and other characterization equipment and high temperature tensile test methods,the relationship between the properties and the structure of refractory aluminum alloy was deeply studied,and the refractory mechanism and the effect of Mo on the structure and mechanical properties of refractory aluminum alloy were discussed,which provided the basis for the final composition design and practical production of refractory aluminum alloy.The main research results are as follows:For Al-Mg alloy,when Mo content is less than 0.08%,the grain morphology of cold-rolled Al-Mg alloy is fibrous,and no Al₁₂Mo crystal phase is found in the microstructure,and the material properties are good.When the content of Mo increased to 0.17%,the grain morphology of the rolled plate did not change significantly,Al₁₂Mo crystal phase can be found in the microstructure,and the solid solution strengthening effect and strength of the alloy decreased.When Mo content increased to 0.37%-0.53%,the amount of crystalline phase of Al₁₂Mo increased and recrystallized,and the strength decreased.When Mo content increased to 0.86%,the amount of crystalline phase of Al₁₂Mo increased further,but the recrystallization degree of rolled plate decreased due to the enhanced inhibitory effect of semi-coherent Al₁₂Mo diffusion relative to recrystallization,and the material properties were better.The material strength decreased with the increase of tensile temperature,and the high temperature strength was obtained when Mo content was0.08%and 0.86%,which was mainly related to the high temperature stability of semi-coherent Al₁₂Mo dispersion phase.The addition of Mo element in Al-Mg-Si alloy can inhibit the growth of recrystallization,inhibit the reduction of dislocation during solution aging treatment,and increase the contribution of dislocation to strength.The alloy with Mo content of0.39%has the most obvious effect.However,excessive Mo content will form a large amount of coarse Al₁₂Mo crystal phase,and there are more Si elements in the crystal phase,which is not conducive to the improvement of material properties.Based on the high temperature resistance of Al₁₂Mo dispersion phase,Mo alloyed Al-Mg-Si alloy has good mechanical properties at high temperature,and the high temperature tensile strength can be increased by 33%-60%.When Mo content is 0.39%,the tensile strength at room temperature can be increased by 85%to 278 MPa.