Effect of Rolling Orientation on the Microstructure and Mechanical Properties of AZ31B Mg Alloy

The magnesium AZ31B alloy has been utilized in a variety of applications within the automotive and aviation industries due to its high specific strength, low-cost processing, and low density. However, the AZ31B alloy generally has poor ductility and limited workability at room temperature. The objective of this study was to develop a manufacturing processing technique to increase the potential uses of this alloy. The methodology includes cold rolling and annealing using small pass reductions until the samples reached a final thickness of 1.78 mm (0.07 in). The samples were cut into 10.16 mm (0.4 in), 7.62 mm (0.3 in), and 5.08 mm (0.2 in) thicknesses prior to cold rolling and were rolled in 0-, 45-, and 90-degree rolling directions. The grain shapes and sizes were examined via optical microscopy. Tensile testing was conducted to determine the strength and ductility. Scanning electron microscopy (SEM) images were taken to evaluate fractured surfaces. All processes including rolling direction and furnace cooling or air cooling after annealing produced similar results of medium strength (245-250 MPa in ultimate strength, 122-127 MPa in yield) and greater than 22.5% elongations in very thin sheets. Samples rolled along the 45-degree direction produced the highest percent reduction in thickness.

Low-Cycle Fatigue Behavior of Hot-Bent Basal Textured AZ31B Wrought Magnesium Alloy

In the recent past, several researchers have successfully modeled the complex fatigue behavior of planar twin-roll cast AZ31B alloy sheets. Complex components are usually hot-bent, whereby the microstructure in the hot-bent areas changes significantly. However, studies on the fatigue behavior of hot-bent magnesium alloys are currently lacking. Therefore, a novel, uniaxial hot-bent specimen was developed and optimized with finite element method simulations. Microstructural analyses with the electron backscatter diffraction method reveal that the hot-bending process changes the texture and increases the Schmid factor for basal slip in rolling and transverse direction of the sheet. In the subsequent quasi-static tension and compression tests, anisotropic and asymmetric yield stresses, lower Young’s moduli compared with the as-received material and macroscopic bands of twinned grains are obtained. Finally, the study proves that the recently proposed concept of highly strained volume can accurately estimate the lifetime, even by combining the as-received and hot-bent material in one fatigue model.

Study of the performance parameters of friction stir welded magnesium AZ31B alloy at optimized process parameters

The present study is aimed to analyze the effect of process parameters on the qualities of the Friction Stir Welded AZ31B Mg Alloy. Response Surface Methodology based Grey Relation Analysis technique was used to multi-optimization of the response parameters such as tensile strength (TS), percentage elongation (El), microhardness (MH), and impact strength (IMP). The mathematical models for response parameters were developed by considering tool rotational speed (RS), tool shoulder diameter (SD), and welding speed (WS) as process parameters. ANOVA (Analysis of Variance) was performed to check the adequacy of the formulated mathematical model and figure out the significant parameters. The results revealed that RS of 950 rpm, WS of 150 mm/min, and SD of 11 mm are the optimal process parameters for optimum response parameters (TS of 157.8700 MPa, IMP of 4.3001 Joule, MH of 84.1335 Hv, and El of 10.0071%). WS is the most significant factor, followed by RS and SD. The grain growth was observed in thermo-mechanically affected zone (TMAZ). The fracture analysis indicated that crack had initiated from the bottom of the centerline in the welded zone and propagated towards the advancing side.

Design and Multidimensional Screening of Flash-PEO Coatings for Mg in Comparison to Commercial Chromium(VI) Conversion Coating

REACH (Registration, Evaluation, Authorisation and Restriction of Chemicals) regulations demand for an expedient discovery of a Cr(VI)-free alternative corrosion protection for light alloys even though the green alternatives might never be as cheap as current harmful technologies. In the present work, flash- plasma electrolytic oxidation coatings (FPEO) with the process duration < 90 s are developed on AZ31B alloy in varied mixtures of silicate-, phosphate-, aluminate-, and fluoride-based alkaline electrolytes implementing current density and voltage limits. The overall evaluation of the coatings’ anticorrosion performance (electrochemical impedance spectroscopy (EIS), neutral salt spray test (NSST), paintability) shows that from nine optimized FPEO recipes, two (based on phosphate, fluoride, and aluminate or silicate mixtures) are found to be an adequate substitute for commercially used Cr(VI)-based conversion coating (CCC). The FPEO coatings with the best corrosion resistance consume a very low amount of energy (~1 kW h m−2 µm−1). It is also found that the lower the energy consumption of the FPEO process, the better the corrosion resistance of the resultant coating. The superb corrosion protection and a solid environmentally friendly outlook of PEO-based corrosion protection technology may facilitate the economic justification for industrial end-users of the current-consuming process as a replacement of the electroless CCC process.

Interfacial Morphology and Bonding Mechanism of Explosive Weld Joints

Interfacial structure greatly affects the mechanical properties of laminated plates. However, the critical material properties that impact the interfacial morphology, appearance, and associated bonding mechanism of explosive welded plates are still unknown. In this paper, the same base plate (AZ31B alloy) and different flyer metals (aluminum alloy, copper, and stainless steel) were used to investigate interfacial morphology and structure. SEM and TEM results showed that typical sine wave, wave-like, and half-wave-like interfaces were found at the bonding interfaces of Al/Mg, Cu/Mg and SS/Mg clad plates, respectively. The different interfacial morphologies were mainly due to the differences in hardness and yield strength between the flyer and base metals. The results of the microstructural distribution at the bonding interface indicated metallurgical bonding, instead of the commonly believed solid-state bonding, in the explosive welded clad plate. In addition, the shear strength of the bonding interface of the explosive welded Al/Mg, Cu/Mg and SS/Mg clad plates can reach up to 201.2 MPa, 147.8 MPa, and 128.4 MPa, respectively. The proposed research provides the design basis for laminated composite metal plates fabrication by explosive welding technology.

Biological evaluation of selective laser melted magnesium alloy powder

Purpose: The current study examined magnesium alloy AZ31B specimens manufactured with Additive Manufacturing method (selective laser melting – SLM) to investigate the applicability of this technology for the production of medical devices. Methods: Osteoblast cells and bacterial biofilm growth ability on specimen was examined and the effect of surface state on corrosion resistance was evaluated by electrochemical and immersion methods. Results: High survival of hFOB cells, as well as a strong tendency for Pseudomonas aeruginosa and Staphylococcus aureus biofilm proliferation on the surface of the tested specimens were shown. SLM-processed AZ31B alloy has a higher corrosion resistance in 0.9% NaCl solution and in a multi-electrolyte saline solution than the material in a conventional form of a rolled sheet. Conclusions: It has been demonstrated that the strong development of the surface of as-built processed specimens results in a significantly increased corrosion rate, which hinders the production of complex structures in tissue engineering products that support cell ingrowth.