Papers by Keyword: AZ91 Mg Alloy

Abstract: High velocity arc spraying (HVAS) process was used to deposit Al-Ni-Y-Co and Al-Ni-Mm-Fe amorphous/nanocrystalline composite coatings onto AZ91 Mg alloy substrate. Their microstructure was characterized by using X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The coatings are both about 500 μm in thickness with fully dense and low porosity. The microstructure of the coatings is classified into two regions, namely, a full amorphous phase region and homogeneous dispersion of fcc-Al and some intermetallic nanoscale particles in a residual amorphous matrix region. Vickers micro hardness of the coatings was also measured. The average Vickers micro hardness of Al-Ni-Y-Co and Al-Ni-Mm-Fe coating is about 311 HV and 340 HV, respectively.

Abstract: In this paper, the commercial AZ91 Mg alloy with mixed rare earth (RE) Y、Gd and Nd has been investigated and effects of RE on die-casting microstructure and properties of die-casting Mg alloy has been also explored. The results indicate that RE can effectively refine the grain size of the alloy and improve inner microstructures transforming the reticular structure of Mg₁₇Al₁₂ phrase into granular or dotlike structure. At the same time, the amount of the compound at crystal boundary is less than that in the alloy without RE. In addition, the mechanical properties of AZ91 Mg alloy with mixed RE has been improved efficiently, and its tensile strength s_b can reach over 260MPa; its elongation δ can also reach over 4.5％. When the amount of mixed RE exceeds 5%, it will form coarse Al-RE compounds, which can low the mechanical properties of Mg alloy.

Abstract: Carbon Nano Tube (CNT) reinforced AZ91 metal matrix composites (MMC) were fabricated by the squeeze infiltrated method. Properties of magnesium alloys have been improved by impurity reduction, surface treatment and alloy design, and thus the usage for the magnesium alloys has been extended recently. However there still remain barriers for the adaption of magnesium alloys for engineering materials. In this study, we report light-weight, high strength heat resistant magnesium matrix composites. Microstructural study and tensile test were performed for the squeeze infiltrated magnesium matrix composites. The wear properties were characterized and the possibility for the application to automotive power train and engine parts was investigated. It was found that the squeeze infiltration technique is a proper method to fabricate magnesium matrix composites reducing casting defects such as pores and matrix/reinforcement interface separation etc. Improved tensile and mechanical properties were obtained with CNT reinforcing magnesium alloys

Abstract: The effect of Ca and Sr content on the microstructure and mechanical properties of a cast AZ91 magnesium alloy is investigated. Ca and Sr additions in AZ91 magnesium alloy are expected high creep resistance. The microstructure of the alloy exhibits the dendritic α-matrix and the second-phases forming networks on the grain boundary. Tensile tests at elevated temperatures between 448 and 523K reveal that the creep resistance was improved with increasing the additional amount of Ca, especially more than 1.0wt%. From the perspective of grain refinement effect, it is expected that the additions of Ca and Sr to AZ91 magnesium alloy not only improve creep resistance but also improve mechanical properties at room temperature.

Abstract: Effect of pulsed high-energy electron beam on the surface modification and the state of surface layer and wear resistance of AZ91 magnesium alloy have been investigated in this study. Optical microscope (OM) and X-ray diffraction (XRD) were employed to characterize the microstructure and phase composition of the modified surface layer. It was found that the thickness of melted layer on the surface varied with electron beam current and the numbers of pulses, the treated surface layer exhibited higher hardness than AZ91 alloy. The friction coefficient and the wear volume of AZ91 alloy after electron beam treatment decrease markedly. The wear resistance of treated samples were significantly improved, which may be attributed to high hardness as a result of grain refinement.

Abstract: Effects of CaCO3 modificator on microstructure and mechanical properties of cast AZ91 Magnesium alloy have been investigated. Tensile fracture behavior of AZ91 alloys modified by CaCO3 has also been studied. Results show that CaCO3 modificator can obviously refine the grain of AZ91 magnesium alloy and Mg17Al12. Mg17Al12 in grain boundary of AZ91 alloy after modified by CaCO3 changes from continuous reticular structure to discontinuous reticular structure, even so much as granular structure and rod structure. After modified by 0.5wt% CaCO3 modificator, ultimate tensile strength, yield strength, impact toughness and elongation of AZ91 alloy increase from 186MPa to 200MPa, from 147MPa to 160MPa, from 4J to 9J and from 2.6% to 5%, respectively. And 0.5wt% CaCO3 modificator brings about an optimal refining effect. The study also shows that the fracture mechanism of modified AZ91 alloy is between cleavage fracture and quasi-cleavage fracture, which is as same as that of unmodified AZ91 alloy.

Abstract: Semi-solid AZ91 magnesium alloys were produced using a cooling plate followed by quenching in the mold. The cast and T6 heat treated microstructures were microscopically characterized and subjected to hardness tests. It was found that the resultant microstructure in water quenched semi-solid specimen were finer than that in conventional permanent mold cast specimen. The hardness tests also showed that the hardness of quenched semi-solid cast specimen was higher than that of permanent mold cast specimen. This was attributed to large amount of precipitates which results from fine precipitation of eutectic phase at intergranular areas during the aging treatment after its complete dissolution.

Abstract: This study is concerned with the effect of high energy ion beam irradiation on surface properties of AZ91 magnesium alloy. The study included a characterization of ion beam surface modification zone in terms of microstructure, and mechanical properties like nanohardness, wear, and corrosion resistance of the surface layer were studied in details. Nanohardness of the modification layer was improved about 2 times as that of the as-received AZ91. The corrosion resistance of the modified layer was significantly improved in NaCl solution because of refined grains. The wear resistance of the modification layer was also improved as compared to as-received AZ91.

Abstract: Various amounts of antimony and mischmetal (Ce-rich) were added into AZ91 cast magnesium alloy and the microstructural characteristics of the cast magnesium alloys were studied by optical microscopy, electronic microscopy and X- ray diffraction techniques. Both antimony and mischmetal had grain refinement effect to AZ91 alloy. When they were added together, a further refinement was observed. SEM-EDX and XRD analysis indicated that a plate-shaped phase, Al11RE3, formed at the boundaries of dendritic α-Mg grain. A rod-like Mg3Sb2 compound distributed both within α -Mg dendrites and along grain boundaries. A new spherical particle, ReSb, formed in the magnesium alloy when 0.8wt%RE and 0.4wt%Sb were join added. The individual additions of antimony or mischmetal to AZ91 alloy did not result in a noticeable improvement to its room temperature tensile properties, but when 0.8wt%RE and 0.4wt%Sb were added together, the as-cast tensile properties of the alloy were increased dramatically.

Abstract: Friction stir welding of dissimilar formed Mg alloys(AZ31/AZ91) was successfully carried out at the limited welding conditions. In a sound joint, SZ was mainly consisted of AZ31 Mg alloy which was located the retreating side. Dynamic recrystallization and grain growth occurred and β intermetallic compounds of AZ 91 Mg alloy was not observed in SZ. BM had a higher hardness than that of the weld zone. The fracture location was not weld zone but BM of the AZ91 Mg alloy in tensile test.