Effect Of Sb On Microstructure And Damping Capacity Of Mg-8Zn-4Al-0.3Mn Magnesium Alloy

AZ91 alloy which is widely used at the present time has many advantages, such as high ambient temperature strength, good casting property and low cost. However it is unsuitable for use at temperatures above 120 degree due to its poor mechanical properties at elevated temperature. Although Mg-Al-Si and Mg-Al-RE alloys were developed for application at elevated temperature, their limited castability or higher cost has restricted their casting applications. Therefore, it is important to develop some new magnesium alloys with low cost and high mechanical properties at room and elevated temperature. The alloy of Mg-8Zn-4Al-0.3Mn system is promising to meet the above requirements.The low cost Sb is an alloying element that has better prospect of application in magnesium alloys. At present, it has been used in the AZ91 magnesium alloy to improve its heat resistance. However, the effect of Sb on the Mg-8Zn-4Al-0.3Mn magnesium alloy was not reported inside and outside of China. Otherwise, the damping capacity of magnesium is the best in the metallic materials. The mechanical properties of magnesium alloys can be impro-veed by modification treatment obviously. Nevertheless, study of effect of modification treatment on the damping capacity is very few.In this thesis, the influents of adding various amount of Sb and conducting different heat treatment processes on microstructures and damping capacity of Mg-8Zn-4Al-0.3Mn based alloy was studied by using measurements of Optical Microstructure(OM), X-ray Diffraction(XRD), Scan Electric Microscopy(SEM), Energy Dispersive Spectrometer(EDX ), Micro-hardness test and Dynamic Mechanical Analysis(DMA).The as-cast microstructure of Mg-8Zn-4Al-0.3Mn has been investigated. The results show that: (1) the microstructures of Mg-8Zn-4Al-0.3Mn based alloys with Sb addition is consisted of matrix - a(Mg) supersaturating solid solution, white t(Mg32(Al,Zn)49) and Mg3 AlZne ternary-phases and black-gray eutectic a(Mg) phases. (2) two new phases(Mg3A!Zn6 and MgaSbi) were formed in the alloys with Sb addition compared with the alloy without Sb addition.(3)the microstructure of Mg-8Zn-4Al-0.3Mn alloy can be refined obviously by the addition of 0.3wt%Sb. Its grain size reduces from 120~130m in the original alloy to 50~60 m. (4) the morphology of (Mg32(Al,Zn)49) and (Al2Mg5Zn2) ternary-phases on the grain boundaries changes from quasi-continuous net-shape of the original alloy to discontinuous-shape and the distribution of ternary-phase in the alloy with 0.3wt%Sb addition is uniform relatively. (5) the micro-hardness values of matrix of alloys increase with the increasing of Sb addition. The micro-hardness peak-value increment of the matrix of Mg-8Zn-4Al-0.3Mn-xSb alloy reaches 2.6%,6.9%,8.8%,9.8% and 11.5%respectively with the addition of 0.1%,0.2%,0.3%,0.4% and 0.5%Sb. (6) the addition of Sb can promote the diffusion of the atoms of Al and Zn to eutectic a(Mg). The matrix contents of Al and Zn atoms increase with the increasing of Sb addition.The results of heat treatments show that: (1) the distribution of ternary phases in the matrixes of alloys with Sb addition are more uniform than the original alloy after the heat treatment of 12 hrs. (2) compared with the alloy without modification, micro-hardness peak-values have obvious improvement after the heat treatment. The increment of micro-hardness peak-values of alloys is 4.45%, 7.04%, 13.36%, 4.74 and 4.45% with the addition of 0.1%,0.2%,0.3%,0.4% and 0.5%Sb respectively. The micro-hardness of alloy with 0.3 wt% Sb is the highest at the condition of heat treatment. (3) the micro-hardness of alloy with Sb addition can be improved by aging obviously. The micro-hardness of alloy with 0.3wt% Sb is the highest after aging. In a word, as the time increasing, the micro-hardness of alloys present the changing rule of increasing first and then decreasing and the micro-hardness peak-values of alloys is obtained at a aging time of 8 hrs.The results of damping capacity show that: (1) the addition of Sb decreases the low temperature damping prope...