关键词： Age hardening  

摘要： To enable broader applications of magnesium alloy sheets, one requirement is to achieve comparable strength-formability balance with that of aluminum-based alloys. Based on the review of recent studies on precipitation hardening of microalloyed magnesium alloys, we propose the usage of age-hardenable alloys to overcome the strength-formability trade-off in magnesium alloy sheets. Precipitation hardening has not been actively used in commercial wrought magnesium alloys because of their poor age-hardening responses. However, recent studies have shown appropriate selection of microalloying elements leads to a substantial enhancement of the kinetics of age-hardening. We found Mg-Ca-X (X = Al, Zn) dilute alloys show promising age-hardening characteristics for bake-hardenable alloy sheets that may be used as a substitute for 6xxx aluminum alloy sheet for weight reduction. Such alloys show excellent room temperature stretch formability, and substantial strengthening to similar to 240 MPa can be achieved by a short-term aging at low temperatures: 170 degrees C for 20 min.

关键词： magnesium alloy   AM60   biobased coating   PA11   silicon-based coating   polyester lacquer   food contact   chemically aggressive environment   specific migration  

摘要： Low-cost, environmentally friendly and easily applicable coating for Mg alloys, able to resist in real world conditions, are studied. Coatings already used for other metals (aluminum, steel) and never tested on Mg alloy for its different surface and reactivity were deposited on AM60 magnesium alloys to facilitate their technological applications, also in presence of chemically aggressive conditions. A biobased PA11 powder coating was compared to synthetic silicon-based and polyester coatings, producing lab scale samples, probed by drop deposition tests and dipping in increasingly aggressive, salty, basic and acid solutions, at RT and at higher temperatures. Coatings were analyzed by SEM/EDX to assess their morphology and compositions, by optical and IR-ATR microscopy analyses, before and after the drop tests. Migration analyses from the samples were performed by immersion tests using food simulants followed by ICP-OES analysis of the recovered simulant to explore applications also in the food contact field. A 30 mu m thick white lacquer and a 120 mu m PA11 coating resulted the best solutions. The thinner siliconic and lacquer coatings, appearing brittle and thin in the SEM analysis, failed some drop and/or dipping test, with damages especially at the edges. The larger thickness is thus the unique solution for edgy or pointy samples. Finally, coffee cups in AM60 alloy were produced, as real word prototypes, with the best performing coatings and tested for both migration by dipping, simulating also real world aging (2 h in acetic acid at 70 degrees and 24 h in hot coffee at 60 degrees C): PA11 resulted stable in all the tests and no migration of toxic metals was observed, resulting a promising candidate for many real world application in chemically aggressive environments and also food and beverage related applications.

关键词： Magnetic abrasive finishing (MAF)   Removal mechanism   Mutual suitability   Spherical composite magnetic abrasive particles   Aluminum and magnesium alloys  

摘要： In this paper, the magnetic abrasive finishing (MAF) on AZ31B magnesium alloy and 7075-T6 aluminum alloy was carried out, using the spherical composite magnetic abrasive particles (MAPs) prepared by our research group independently. The finishing experiments were conducted by using the Al2O3/Fe-based MAPs and SiC/Fe-based MAPs, respectively. The results of our works show that there are disparities in the mutual suitability between the MAPs with different abrasive phase and the processed materials. After finishing, the surfaces of workpieces with the foggy mirror effect are obtained. The effects of MAF with different abrasive phase on the surface quality were investigated. The material removal mechanism and surface formation processing of workpieces in MAF were analyzed. The conclusion is as follows: in MAF processing, under the combined action of plastic deformation flow, skiving, extrusion, and chemical reaction, the surfaces of workpieces meet the requirements of surface quality.

关键词： Friction stir butt welding   Mg/steel dissimilar metal   Truncated cone-shaped stirring pin   Steel-strip  

摘要： A truncated cone-shaped stirring pin with threads was designed to enhance friction stir butt welding (FSBW) quality of AZ31B magnesium alloy and Q235 low carbon steel. The effects of welding speed and rotation speed on the microstructure and properties of joints were studied. Microstructure characteristics and element distribution along the Mg/steel interface were analyzed. The results showed that the truncated cone-shaped stirring pin with threads effectively improves the metal flow behavior, especially the fluidity of steel. A steel-strip was formed at the bottom of the Mg side weld nugget during the welding process. The stirring pin effectively improved the interfacial reaction at the Mg/steel dissimilar metal. A thin accumulation layer of the Al was observed along with the interface. Discontinuous oxides of Mg appeared in the interface and were mainly distributed in the upper and bottom interfaces of the joint. As the heat input increased, the metallurgical bonding of the Mg/steel interface became stronger, and the joint strength increased. But when the heat input increased to a certain level, the oxidation of the Mg/steel interface became serious. The aggregation of MgO in the Mg/steel interface led to cracks, which decreased the joint strength. When the welding speed was 75 mm/min and the rotation speed was 850 rpm, the highest tensile strength of the joint was 189.4 MPa, which is 75.8 % of magnesium alloy. The joint fractured in the Mg side near the Mg/steel interface.

关键词： cerium‐   based conversion coating   corrosion resistance   KMnO4   Mg–   4Y–   2Al alloy  

摘要： The cerium salt chemical conversion baths containing KMnO4 are applied to prepare protective coatings on the WA42 alloy surface, and the effect of the concentration of KMnO4 on the microstructure and corrosion properties of the coatings is investigated by scanning electron microscopy, X-ray photoelectron spectroscopy, and electrochemical tests. The results indicate that with the addition of KMnO4 to the conversion bath, the microstructure of the coating is more uniform and denser, and the coating with the KMnO4 concentration of 4 g/L (4M coating) has the most uniform microstructure with the least microcracks. The 4M coating exhibits a two-layered structure, and it is mainly composed of MgO, Mg(OH)(2), CeO2, Ce2O3, Ce(OH)(3), MnO, and MnO2. In addition, as the KMnO4 concentration increases from 0 to 6 g/L, the I-corr of the coatings in 3.5% NaCl solution decreases first and then increases, and the 4M coating shows the best corrosion resistance, which should attribute to the uniform and dense microstructure.

关键词： Magnesium alloy   Twinning   Non-basal slips   Strain hardening   Stress state  

摘要： Stress-strain responses and twinning characteristics are studied for a rolled AZ31B magnesium alloy under three different stress states: tension along the normal direction (NDT), compression along the rolled direction (RDC), and torsion about the normal direction (NDTOR) using companion specimens interrupted at incremental strain levels. Tension twinning is extensively induced in twinning-favorable NDT and RDC. All the six variants of tension twin are activated under NDT, whereas a maximum of four variants is activated under RDC. Under NDTOR, both tension twins and compression twins are activated at relatively large strains and twinning occurs in a small fraction of favored grains rather than in the majority of grains. Secondary and tertiary twins are observed in the favorably-orientated grains at high strain levels. Deformation under each stress state shows three stages of strain hardening rate: fast decrease (Stage I), sequential increase (Stage II), and progressive decrease (Stage III). The increase in the hardening rate, which is more significant under NDT and RDC as compared to NDTOR, is attributed to the hardening effect of twin boundaries and twinning texture-induced slip activities. The hardening effect of twin boundaries include the dynamic Hall-Petch hardening induced by the multiplication of twin boundaries (TBs) and twin-twin boundaries (TTBs) as well as the hardening effect associated with the energetically unfavorable TTB formation. When the applied plastic strain is larger than 0.05 under NDT and RDC, the tension twin volume fraction is higher than 50%. The twinning-induced texture leads to the activation of nonbasal slips mainly in the twinned volume, i.e. prismatic slips under NDT and pyramidal slips under RDC. The low work hardening under NDTOR is due to the prevailing basal slips with reduced twinning activities under NDTOR.

关键词： AZ80 magnesium alloy   Processing map   Isothermal forging   DRX   PSN  

摘要： The hot deformation behavior of pre-forged AZ80 magnesium alloy is investigated by the isothermal compression tests at temperatures of 523-683 K and strain rates of 0.0001-0.1 s(-1), and analyzed by the processing maps for guiding isothermal die forging. Flow localization and even cracking occurs at low temperatures and high strain rates, where shear deformation degree shows a positive correlation with the xi

关键词： Magnesium alloy   Energy efficiency   Metal forming   Vaporizing foils  

摘要： Vaporizing metal foils is a relatively new high-speed material processing technique which can improve the material's forming limit and reduce the springback. This study aims to investigate the forming behaviors of sheet metals by vaporizing metal foils. A simple analytical model to calculate the energy efficiency of this forming method is firstly introduced. The forming behaviors of magnesium alloy AZ31 is analyzed by free bulging tests at room temperature. Besides, the mechanical behaviors of magnesium ally AZ31 is compared with that of aluminum alloy EN AW-6082. The experiments indicate that the magnesium alloy AZ31 exhibits good formability by vaporizing metal foils without heating treatment. Therefore, it is feasible to conduct plastic forming process of magnesium alloy ZA31 at room temperature, which is different from the traditional warm forming method for magnesium alloy.

关键词： plasma electrolytic oxidation   alumina nanoparticle   wear   corrosion  

摘要： The synthesis of ceramic coatings via conversion of metallic surface is the main route of corrosion resistance in the magnesium alloys. Using ceramic nano-particles as sealant in these coatings is very useful. In this study, the effect of applied current density and treatment duration on the alumina nanoparticle incorporation, corrosion resistance, and wear behavior of plasma electrolytic oxidation coating on AZ31 alloy was investigated. The results showed that the highest incorporation of nanoparticles occurs at a current density of 100 mA/cm(2) during 10 min while at higher current densities or treatment durations, the eruption of molten oxide prevents the embedding of nanoparticles inside the coating. The high incorporation of nanoparticles increased the homogeneity and compaction of the coating which caused the highest corrosion and wear resistance.