Materials Science Forum Vols. 610-613

Abstract: When Mg-10(wt.%)Sb alloy was melted, the alloy melt was into two tiers. The semisolid formed in the bottom of the melt became Mg-13Sb alloy and the upper of the melt became Mg-9Sb alloy. Both of Mg-9Sb and Mg-13Sb alloys consist of α-Mg phase and α-Mg3Sb2 precipitates which distributed homogenously in the matrices. In Mg-9Sb alloy, two types of precipitates are observed, the majority rod-shaped and the minority rectangle-shaped. In Mg-13Sb alloy, all of the precipitates were just block.

Abstract: Titanium dioxide (TiO2) and silicon dioxide (SiO2) coating deposition were respectively performed by the dip coating technique on magnesium AZ31 alloy with extrusion surface finishes. The anticorrosive effect of different sol-gel coating was compared by measuring the weight loss when the samples were immerged in atmosphere, acetic acid aqueous solution with pH 5.0, distilled water with pH 6.4, aqueous 5% sodium chloride solution with pH 7.0. Morphological and structural characteristics of the coatings were analyzed by scanning electron microscopy (SEM), and semi quantitative analyses of the composition were performed by energy dispersive X-ray analysis (EDX) line scans. The results show that the anticorrosion properties of magnesium alloy with SiO2 or TiO2 are magnificently impactful in atmosphere. The anticorrosion effect of TiO2 coating is much preferable in a relatively strong acid environment.

Abstract: An anticorrosion conversion coating on metal magnesium surface was prepared using immersion method in an aqueous solution containing mainly phytic acid. The coating after the preparation could be dry in the air without a rinse process using water in the final stage. Hence there is no discharge of waste water and waste gas in the whole process. Influence of several factors on the anticorrosion performance of coating was tested. And optimal parameters in the coating formation process were obtained from orthogonal test. The results indicated that the coating had better corrosion resistance, when the solution contained 3% phytic acid, and the immersion time is 7 minutes and the PH value was 3.5. The surface conversion coating was characterized by SEM and EDS. The conversion coating is better than the traditional chromate passive film by testing corrosion speed of coatings using hydrogen evolution method. The technology of the environment-friendly conversion coating containing phytic acid has the potential to be a new anti-corrosion technology for magnesium surface.

Abstract: The microstructure, mechanical properties, hardness, rules and mechanism of various parameters on formation of weld bead of Mg alloy ACM522 using a fiber laser welding were investigated. The results showed that sound welds without major defects could be produced and the mechanical properties of welding joints were good. With the increase of laser power, the penetration depth and bead width of the weld bead all increased. The mechanism of welding transformed from the conduction welding mode to the deep penetration welding mode and the weld beads aspect ratio became higher with the increase of heat input. The microstructure of weld metal was significantly finer and the hardness of weld metal was higher than that of the base metal.

Abstract: Magnesium alloy matrix quality is important for the quality of coating on the surface, and thus affecting the final performance of magnesium alloy. This paper developed a method to the abrasive belt grinding as a pre-treatment process for magnesium alloy. Based on the orthogonal test in the abrasive belt grinding of magnesium alloy, the effect of the processing parameters on grinding force and roughness has been studied. Finally, a predicting model of the grinding force and surface roughness was established by means of the neural networks. This model was verified from both the theoretical and experimental facets. The results showed that the model can be used to describe the influence of some machine tool inputs

Abstract: With the aim of evaluating corrosion inhibition for various inhibitors, a new qualitative method for corrosion inhibition effect test for magnesium and magnesium alloys was developed. The change of polarization current density of AZ61 magnesium alloy in electrochemical polarization experiments in alkali aqueous solution with 5mmol/L sodium dodecylsulphate(SDS), phytic acid(PA), ethylenediamine tetraacetic acid(EDTA), p-nitro-benzene-azo-resorcinol(PNBAR), acidum tannicum(AT) or stearic acid(SA) were tested. The SEM-EDS techniques and deposition experiment method were used for further confirmation of the corrosion inhibition. The results showed that those organic compounds which could form the inhibitor-magnesium precipitation in aqueous solution could be used as corrosion inhibitors for magnesium alloys to inhibit the increase of polarization current density as well as the dissolution and oxidation of magnesium alloys effectively.

Abstract: Silane treatment is an effective method of chemical conversion as a replacement for chromium treatments. In this paper, KH-550 silane treatment was adopted to improve the corrosion resistance AZ31 magnesium alloy. Hydrolysis process of KH-550 in the silane solutions was detected by the conductivity detection method. It was found that KH-550 silane could be hydrolyzed easily and its hydrolysis time was about 10 minutes. Polarization curve and salt immersion were carried out to investigate the corrosion behavior of the coated magnesium alloy treated by five kinds of silane solutions with different silane concentrations. When the concentration of KH-550 in the silane solution was 8%, the coated specimens by heating at 100°C for half an hour after the surfaces dry had more excellent corrosion resistance than others. It was shown that the KH-550 silane treatment could form a -Si-O-M covalent bonded film/metal interface and -Si-O-Si siloxane chains to improve the corrosion resistance of coated magnesium alloy.

Abstract: In this study, taking die-cast magnesium alloy AZ91D as investigation objects, the process characteristics of electron beam welding (EBW) was studied. The microstructure and familiar defects in the welded joints were analyzed. The main reasons of these defects were discussed. The experimental results showed that boundary surface between fusion zone and heat affected zone in the joint of AZ91D magnesium alloy by electron beam welding is obvious, the fusion zone (FZ) consisted of fine-equiaxed grain. Pore and crack are the main defects in AZ91D magnesium alloy joints. Magnesium has higher hydrogen solubility in liquid than in solid. The difference in the solubility between the solid and liquid phase is the major reason of the pore of magnesium alloys during welding. The crack was caused because of α + β-Mg17Al12 phase with low melting point and pores in the fusion zone. There were other defects found in the joints such as incomplete fusion and penetration.

Abstract: This paper deals with an environment-friendly anodizing oxidation process for AZ31 magnesium alloy. Good anti-corrosion anodizing oxidation coating was prepared on the surface of AZ31 magnesium under 10 mA/cm2 constant current at 20°C after 20 min. The anodic film of AZ31 was ivory-white, dense, uniform, compact and porous structure. The anodic film of AZ31 mainly consisted of MgO, Mg2SiO4.According to Tafel curve and EIS,the anodic film of AZ31 had better anti-corrosion property than the substrate AZ31. This anodic film could increase the anti-corrosion property of AZ31 effectively.

Abstract: The corrosion and degradation behavior of Mg-Ca binary alloy in simulated body fluid (SBF) were studied by immersion of pure Mg and Mg-Ca alloys with different Ca contents in SBF. The corrosion process was carried out by real-time measurement of sample weight, pH value of SBF and the microstructures of the immersed samples at different immersion time observed by electron microscopy. The result shows that Mg-Ca alloy with 0.7% Ca has better corrosion resistance than the one with 2.0% Ca. The product generated on the surface of Mg-0.7Ca during the immersion was identified by X-ray diffraction and energy spectrum analysis.