Papers by Keyword: Mg Alloy

Abstract: In the present study, a two-dimensional steady state laminar flow model was developed using fluent software in order to investigate the possibility of achieving Mg/Al cladding using a horizontal twin roll caster. The effects of parameters such as upper and lower inlets casting sequence, solidification length on the temperature field at the bond interface and outlet thickness direction were investigated. The feasibility of the model was verified by combining with experiments. The results show that the molten A5052 alloy with a high melting point is more suitable to be cast by the lower roll at the roll speed of 9 m/min and the roll gap of 5 mm. The temperature of the A5052 and AZ91 near the bond interface of the clad strip can be controlled by the solidification length. Numerical simulations can provide guidance for the optimal casting process parameters.

Abstract: We recently proposed a new mechanism to simultaneously improve the strength and ductility of multiphase alloys, named “Anisotropic mechanical property-induced ductilization (AMID)”. In this paper, the variations in tensile deformation behavior of Mg/LPSO extruded alloys depending on the volume fraction of the LPSO phase were examined, to deepen the understanding on AMID. As expected, the work-hardening rate of the Mg/LPSO two-phase extruded alloy increased as increasing in the volume fraction of LPSO phase. This demonstrates the validity of the AMID mechanism. However, the increase in the volume fraction of the LPSO phase decreased the elongation, even though the work-hardening rate was increased in them. The present study revealed that an appropriate amount of Mg grains is necessary to obtain the effect of AMID in improving the uniform elongation of the alloy, by the suppressing the development of microcracks formed in the LPSO phase grains into macroscopic fracture.

Abstract: Cu and Ni impurities in Mg alloys are deleterious contaminants that reduce the corrosion resistance of the alloy. Mg₂Cu and Mg₂Ni precipitates can cause significant anodic dissolution of the Mg matrix, owing to their potential difference. Suppression of these phases can prevent the deterioration of corrosion resistance. The neutralization of these impurities through the formation of MgZn₂ intermetallic phases has been studied, because the atomic radii of Cu and Ni are similar to that of Zn. As a result, the MgZn₂ phase may precipitate during the rapid cooling that occurs during the solidification of the Mg-6 mass% Zn alloy, and introduce substitutional impurity atoms in the crystal lattice. Mg (Zn, Cu, Ni)₂ phase can be formed instead of Mg₂Cu and Mg₂Ni, in the presence of both of Zn and these impurities. In this study, the solubility of Cu and Ni into MgZn₂ phase when they contain simultaneously was investigated by preparing the intermetallic compounds and the crystal structure evaluation. The lattice parameter of the MgZn₂ phase containing both Cu and Ni impurity decreased to about 5.14 Å with increasing impurity concentration. Cu and Ni impurities are concentrated in the MgZn₂ phase while maintaining the crystal structure, when the impurity concentrations are within the composition range of Cu + 2Ni ≦ 20 at.%. When the concentrations of Cu and Ni exceeded this range, the crystal structure of the MgZn₂ phase transformed from hexagonal (hP12) to cubic (cF24).

Abstract: Mg alloys are very attractive materials for transportation industry due to their toughness and lightness. Recycling Mg alloys is desired for energy saving that otherwise would be required to produce its primary metal. However, secondary produced Mg tends to contain a few impurity elements that deteriorate its corrosion resistance. For example, contamination of Mg alloy by Cu induces second phase of Mg₂Cu and it works as strong cathode, resulting in the corrosion rate rapidly increasing. It was previously reported that the corrosion resistance of Mg with impurity Cu was remarkably improved by addition of alloying element Zn. Addition of Zn into Mg formed MgZn₂ phase and incorporated Cu into MgZn₂ phase instead of Mg₂Cu formation. In this way, since Zn serves to improve the corrosion resistance of Mg, Mg alloy with high Zn concentration may form a lot of MgZn₂ and may have better corrosion resistance even with high Cu concentration. In this work, the corrosion behavior of Mg-6mass%-1mass%Al (ZA61) with different Cu content up to 1mass% was investigated. As a result, ZA61-1.0Cu had much lower corrosion rate compared to Mg-0.2%Cu and the corrosion rate was almost the same as that of pure Mg.

Abstract: Recently, mechanochemical multifunction cavitation (MC-MFC) was developed to improve the corrosion resistance of the magnesium surface. MFC is a technology that combines water jet peening and ultrasound cavitation. MC-MFC is a technology that adds phosphoric acid to water. It can improve the corrosion resistance by forming a phosphate film on the Mg surface. Conventional anodic oxidation, plating, and chemical vapor deposition can improve corrosion resistance by forming a film on the Mg surface, but it is difficult to improve characteristics such as compressive residual stress on the surface. MFC-treated surfaces have previously imparted various properties such as imparting compressive residual stress necessary to improve the fatigue strength to Al alloys and Cr-Mo steels. In this study, the effect of film formed on MC-MFC processed surface on compressive residual stress was investigated.

Abstract: An attempt has been made to investigate the microstructures and wear behavior of magnesium alloy AM100 (Mg-Al-Mn) based composites reinforced with 7 vol. % of ZrB₂, graphite or hybrid of (1:1) ZrB₂ and graphite particles as well as the unreinforced magnesium alloy. Magnesium alloy was melt under shield of inert gases and composites were prepared using stir casting method. Optical microscopy was used to study the microstructures of the unreinforced alloy and composites. The composites characterized primarily by the uniform distribution of particles in the matrix and a good adherence between the particles and matrix. XRD analysis was used to identify the phases of the unreinforced alloy and composites. The XRD diffraction pattern of AM100 matrix reveals different phases, namely, Mg, AlMn and Al₁₂Mg_17. Formation of these phases is due to the reaction between alloy constituents. Dry sliding wear tests were conducted by using a pin-on-ring apparatus. The wear rates of the composites and matrix alloy were measured at loads of 10, 20 and 30 N, and sliding speed of 0.7 m/s. The worn surfaces of the composite pins were examined by scanning electron microscopy (SEM). The experimental results of the wear tests showed that the magnesium based composites exhibited higher wear rate at all the applied loads when compared to those of the unreinforced magnesium alloy. The ZrB₂ reinforced magnesium composite exhibited the lowest wear rate amongst the composites material investigated in the present work.

Abstract: In this work, the effect of NaOH concentration on the properties of PEO coatings formed on AZ31B Mg alloy is studied. Composition and structure analysis of coatings were carried out by XRD and SEM. From the results, it was found that the number of pores, defects and width of the discharge traces are highly dependent on NaOH concentration. Major phases of the coating identified from XRD were consisted of MgO and Mg₂SiO₄. The crystallinity of the coatings and magnitude of MgO phase was highly incremented with NaOH concentration. From the Vickers hardness test it was observed that hardness of the coatings prepared in 2g/l of NaOH have the highest values~1050HV, with peak wear resistance values.

Abstract: The phase field models have been built to study the influence of the nonuniform grain boundary energy for abnormal growth of grains in the AZ31 magnesium alloy in the real time and space. The simulated results show that if the grains of a certain orientation with low grain boundary energy in the AZ31 Mg alloy, abnormal grain growth will occur after annealing treatment, and only if the local low grain boundary energy is less than 0.98σ_0, can the certain grains grow abnormally in the microstructure.

Abstract: Plasma sprayed ceramic coatings are successfully employed in many industrial applications, where high wear and corrosion resistance with thermal insulation are needed. Plasma spray parameters such as power, stand-off distance and powder feed rate have significant influence on coating characteristics like deposition efficiency. This paper presents the use of statistical techniques specially response surface methodology (RSM), analysis of variance, and regression analysis to develop empirical relationships to predict deposition efficiency of plasma sprayed alumina coatings on AZ31B magnesium alloy. The developed empirical relationships can be efficiently used to predict deposition efficiency of plasma sprayed alumina coatings at 95% confidence level. Response graphs and contour plots were constructed to identify the optimum plasma spray parameters to attain maximum deposition efficiency in alumina coatings. Further, correlating the spray parameters with coating properties permits the identification of characteristics regime to achieve desired quality of coatings.

Abstract: The microstructure and mechanical responses of the AZ31 with the addition of 1.8% Sn alloys have been studied and compared. Mg alloy sheets were prepared with metal model casting method and subsequent processes by conventional extrusion (CE) and differential speed extrusion (DSE). Mg alloys were hot extruded at 400^oC with the extrusion ratio of 101:1. The microstructure of Mg alloy sheets was examined by optical microscopy (OM) and scanning electron microscope (SEM). The results indicated that the grains were dynamically recrystallized after the extrusion process. Moreover, DSE process dramatically enhanced the room temperature ductility of the extruded sheets. It was also presented that the Mg alloy processed by DSE exhibite a classical dimple structure as a result of slip accumulation and ductile tear.