Lightweight Magnesium Alloys Research Articles

Recent Advances in LPSO-Containing Wrought Magnesium Alloys: Relationships Between Processing, Microstructure, and Mechanical Properties

Development of strong and ductile lightweight magnesium (Mg) alloys has been the subject of enormous research breakthroughs since 2000. This review describes the most significant progress on the design and processing of high-strength wrought Mg alloys containing long-period stacking order (LPSO) phases. It first focuses on the typical atomic structure, transformation, and morphology of various LPSO phases, then explores the key contributions of thermomechanical processing techniques to the metallurgical structure, morphology, spatial dimension, and distribution of diverse LPSO phases and discusses the LPSO-derived strengthening mechanisms of Mg alloys. Finally, future research opportunities for LPSO-containing wrought Mg alloys are proposed on the basis of the mechanistic relationships between the evolution of LPSO phase particles and strengthening mechanisms.

First principles high-throughput screening to enhance the ductility of lightweight magnesium alloys

The low ductility of lightweight magnesium prevents it from wide engineering applications, making it essential to improve its ductility. To provide guidelines to accelerate this improvement, we propose and test a hierarchical high-throughput screening approach for alloy design that is based on the quantum-mechanics-derived full general stacking fault (GSF) energy surface (\ensuremath{\gamma} surface), but simplified to examine only the unstable stacking fault energy (${\ensuremath{\gamma}}_{\mathrm{us}}$). We apply this approach to determine the promising dopant elements in Mg-$X$ binary alloys which may activate the pyramidal dislocations by decreasing GSF energy and thus improve the ductility of Mg. Ten elements, including Hg, Tl, Sn, Sb, Bi, Te, As, Pb, In, and Ca, are sifted out as promising alloying elements. Particularly, the Mg-Te alloy has the lowest ${\ensuremath{\gamma}}_{\mathrm{us}}$ of $156\phantom{\rule{0.16em}{0ex}}\phantom{\rule{4pt}{0ex}}\mathrm{mJ}/{\mathrm{m}}^{2}$ among all binary alloys, which is 25% lower than that of Mg ($209\phantom{\rule{0.16em}{0ex}}\phantom{\rule{4pt}{0ex}}\mathrm{mJ}/{\mathrm{m}}^{2}$), suggesting that it is the most promising alloy to enhance the ductility of Mg.

Recent developments in high-strength Mg-RE-based alloys: Focusing on Mg-Gd and Mg-Y systems

Abstract Higher strength is always the goal pursued by researchers for the structural materials, especially for the lightweight magnesium (Mg) alloys which generally have relatively low strength at present. From this aspect, the present paper reviews the recent reports of a kind of Mg alloys, i.e. Mg-RE (RE: rare earths, mainly Gd or Y) casting and wrought alloys, which have been able to achieve high strength compared with common or commercial Mg alloys, from the viewpoint and content of the alloy system, alloying constitution, preparation process, tensile strength and each of the main strengthening mechanisms. This review of recent research and developments in high-strength Mg-RE alloys is beneficial for the further design of Mg alloys with higher strength as well as excellent comprehensive performance.

A high-resolution synchrotron-based diffraction technique for in situ characterization of deformation behaviour in magnesium alloys

To promote accurate lattice-strain measurement and twinning observation during in situ deformation of age-hardenable lightweight magnesium alloys, a high-resolution X-ray diffraction technique was applied using medium-energy synchrotron X-rays (≤21 keV) coupled with a fast Mythen strip detector. This technique allows data collection in transmission geometry, with sufficient grain-sampling statistics achieved by rocking the samples during each measurement under step-wise uniaxial tensile/compressive loads. The capabilities of the method are demonstrated on a model age-hardenable Mg–Sn-based alloy in compression. The measurements confirm that this technique offers high angular resolution and a wide angular range, minimizing the problem of peak overlap, which is advantageous for accurate lattice-strain determination of both the α-Mg matrix and strengthening precipitate phases. The absolute strain resolution is approximately ±2 × 10−4. Lattice-strain partitioning and anisotropy in the α-Mg phase reveal the occurrence of microplasticity due to the activation of basal dislocation slip in Mg alloys and provide experimental information for characterizing the plastic anisotropy of the materials. The initiation and growth of {10 {\overline 1} 2} tension twins are identified and quantified from the changes in the integrated intensities of 10 {\overline 1} 0/0002 reflections as a function of stress. The critical resolved shear stresses (CRSSs) for the activations of basal slip and tension twin modes in both non-aged and aged materials were estimated. The results reveal that, after the ageing treatment, the CRSS value for basal slip increases from 18 to 33 MPa, an increase of ∼83%, and that for tension twinning increases from 32 to 52 MPa, an increase of ∼63%. The methodology also enables further microstructural data to be probed in situ. This includes the apparent area-weighted twin size and dislocation density during twin onset, and the precipitate volume fraction.

Improving the formability of magnesium by cushion-ram-pulsation

The application of forming processes using lightweight magnesium alloys is known to be difficult with regard to minor formability caused by a small number of active slip systems, especially at low temperatures. However, a new approach for deep drawing at elevated temperatures considers flexible motion profiles of a servo-screw press. The so-called cushion-ram-pulsation (CRP) is a newly developed method of position-controlled motion. As a result, the process limitations for deep drawing are significantly extended. This study investigates the deep drawing process of AZ31 cups by variable motion profiles of cushion and ram, focusing on enhanced drawability. Therefore the initial AZ31 sheet was fabricated by twin-roll casting. Furthermore, the adjustment of the forming temperature for an improved forming process and optimized component properties are described. In addition, the results were evaluated in comparison to conventional deep drawing, and the superior technological potential will be outlined.

Cold‐Sprayed Aluminum‐Silica Composite Coatings Enhance Antiwear/Anticorrosion Performances of AZ31 Magnesium Alloy

Extensive efforts devoted in recent years to booming structural applications of lightweight magnesium alloys are usually undermined by their insufficient surface properties. Surface modification is therefore necessarily required in most cases for enhanced surface integrity of the alloys. Here, we report construction of aluminum‐silica protective layers by cold spray on AZ31 magnesium alloys, and the effect of the silica additives on microstructure and mechanical properties of the coatings was examined. The ceramic particles were dispersed evenly in the coatings, and increased silica content gives rise to enhanced adhesion, antiwear performances, and microhardness of the coatings. The even distribution of silica in the coatings altered the wear regimes from adhesive to abrasive wear. The cold spray fabrication of the aluminum‐silica protective coatings would facilitate structural applications of the magnesium alloys.

Metal Forming of Lightweight Magnesium Alloys for Aviation Applications

AbstractThe work presents an analysis of selected magnesium alloys as structural materials to be used in production of aircraft parts as well as their technological parameters in some manufacturing processes. Upsetting test, backward extrusion and Kobo extrusion of complex cross-sectional profiles and forging process were realized using magnesium alloys AZ31, AZ61, AZ80, WE 43 and Mg alloy with Li for production of thin - walled aircraft profiles and forged aviation parts. The range of temperatures and extrusion rate for the manufacturing these profiles were determined. Tests also covered the analysis of microstructure of Mg alloys in the initial state as well as after the extrusion process. It has been proved that the proper choice of parameters in the case of a specific profile extruded from magnesium alloys allows the manufacturing of products of complex cross-sections and the quality required in aerospace industry. This has been demonstrated on the examples of complex cross-sectional profiles using elements of varied wall thickness and examples of forged aviation parts: aircraft wheel hub and helicopter lever for control system.

Achieving High Strength and Ductility in Magnesium Alloys via Densely Hierarchical Double Contraction Nanotwins.

Light-weight magnesium alloys with high strength are especially desirable for the applications in transportation, aerospace, electronic components, and implants owing to their high stiffness, abundant raw materials, and environmental friendliness. Unfortunately, conventional strengthening methods mainly involve the formation of internal defects, in which particles and grain boundaries prohibit dislocation motion as well as compromise ductility invariably. Herein, we report a novel strategy for simultaneously achieving high specific yield strength (∼160 kN m kg-1) and good elongation (∼23.6%) in a duplex magnesium alloy containing 8 wt % lithium at room temperature, based on the introduction of densely hierarchical {101̅1}-{101̅1} double contraction nanotwins (DCTWs) and full-coherent hexagonal close-packed (hcp) particles in twin boundaries by ultrahigh pressure technique. These hierarchical nanoscaled DCTWs with stable interface characteristics not only bestow a large fraction of twin interface but also form interlaced continuous grids, hindering possible dislocation motions. Meanwhile, orderly aggregated particles offer supplemental pinning effect for overcoming latent softening roles of twin interface movement and detwinning process. The processes lead to a concomitant but unusual situation where double contraction twinning strengthens rather than weakens magnesium alloys. Those cutting-edge results provide underlying insights toward designing alternative and more innovative hcp-type structural materials with superior mechanical properties.

Experimental comparison of energy absorption characteristics of polyurethane foam-filled magnesium and steel beams in bending

Lightweight magnesium alloys and polyurethane foams have attracted much attention in the automotive industry due to their potential to reduce vehicle weight. This study conducted quasi-static/dynamic three-point bending tests to investigate the energy absorption characteristics and deformation behaviour of empty and polyurethane foam-filled magnesium alloy AZ31B thin-walled beams, and to make comparisons with mild steel DC04 beams. The results showed that both deformation/fracture modes and energy absorption capacity of the thin-walled beams subjected to bending loads depend on the strain rate and other parameters, such as the beam material's strength and ductility, foam density and wall thickness. Both the DC04 beams and AZ31B extruded beams showed a positive effect of strain rate on the energy absorption capacity. A beam filled with a higher density foam achieves higher bending resistance, but fractures at a smaller deflection. The experiments demonstrated that AZ31B significantly outperforms DC04 in terms of energy absorption and specific energy absorption for the foam-filled beams, when the beams are subjected to bending loads at a deflection of 250 mm. However, this gain could be weakened when the performance is assessed at a larger fracture deflection because the foam-filled AZ31B beams tend to fracture at smaller deflections. For applications that require limited deformation, there is a possibility to develop lightweight auto-body structures such as rocker rails by substituting foam-filled AZ31B structures for mild steel structures, while maintaining or exceeding their current crashworthiness and safety.

Stifling magnesium corrosion via a novel anodic coating

The use of light-weight magnesium (Mg) alloys as engineering materials has been hampered in part due to their poor corrosion performance. An effective novel sacrificial coating is presented herein.

Direct Single-Stage Processing of Lightweight Alloys Into Sheet by Hybrid Cutting–Extrusion

Widespread application of lightweight magnesium and titanium alloys sheet is limited mainly because of their poor-workability issues, both in primary processing by rolling and secondary sheet forming. This study describes a hybrid cutting–extrusion process, large-strain extrusion machining (LSEM), for producing sheet and foil. By utilizing a constraining edge placed across from the cutting tool edge, the usual cutting process is transformed into continuous shear-deformation process, wherein the thickness of the sheet at its exit from the deformation zone is directly controlled. The confinement of the deformation field in LSEM enables near-adiabatic heating in the deformation zone. Consequently, external workpiece heating, intrinsic to sheet manufacturing by multistage rolling in alloys of poor workability (e.g., hexagonal close packed (hcp) alloys and cast materials), is minimized. Furthermore, the deformation parameters, such as strain, strain rate, and strain path, can be controlled to refine the microstructure and induce shear-type crystallographic textures that enable enhanced sheet mechanical properties (strength and formability). This application of LSEM is demonstrated using magnesium alloy AZ31B as a model system. Since LSEM is a single-stage process for sheet production, it is potentially attractive in terms of production economics and energy. Implications for process scale-up and control of plastic flow localization are briefly discussed.

마그네슘 합금 판재를 활용한 차체 Reinforced Dash 부품 온간성형 공정 연구

The use of light weight magnesium alloy offers significant potential towards improvement of the automotive fuel efficiency. However, the application of formed magnesium alloy components in auto-body structures is restricted due to the low formability at room temperature and lack of knowledge for processing magnesium alloys at elevated temperatures. In this study, a warm tensile test of magnesium alloys was performed to measure tensile strength and elongation. An improvement in formability was confirmed at increased temperatures above about <TEX>$250^{\circ}C$</TEX>. Car body warm forming technology was conducted for forming forming reinforced dash components of the magnesium alloy AZ31B sheet at elevated temperatures.

Fatigue life estimation of ultrasonic spot welded Mg alloy joints

Lightweight magnesium alloys are increasingly used in automotive and other transportation industries for weight reduction and fuel efficiency improvement. The structural application of magnesium components requires proper welding and fatigue resistance to guarantee their durability and safety. The objective of this investigation was to identify failure mode and estimate fatigue life of ultrasonic spot welded (USWed) lap joints of an AZ31B-H24 magnesium alloy. It was observed that the solid-state USWed joints exhibited a superior fatigue life compared with other welding processes. Fatigue failure mode changed from interfacial failure to transverse-through-thickness crack growth with decreasing cyclic load level, depending on the welding energy. Fatigue crack initiation and propagation occurred from both the notch tip inside the faying surface and the edge of sonotrode indentation-footprints due to the presence of stress concentration. A life prediction model for the spot welded lap joints developed by Newman and Dowling was adopted to estimate the fatigue lives of the USWed magnesium alloy joints. The fatigue life estimation, based on the fatigue crack growth model with the global and local stress intensity factors as a function of kink length and the experimentally determined kink angle, agreed fairly well with the obtained experimental results.

Effects of rare element and pressure on the microstructure and mechanical property of AZ91D alloy

Pressurized solidification in combination with grain refinement by rare element was performed for conventional AZ91D magnesium alloy. Both the resultant microstructure and mechanical properties of as-cast ingots were studied. After the addition of 0.75wt% Ce into AZ91D alloy, a comparable grain refinement can be achieved and an acicular phase Al11Ce3 is formed near the grain boundary. Affected by applying certain amount of pressure during solidification process, micro-segregation is weakened and the amount of shrinkage void in the microstructure is reduced due to the enhancement of flow and feeding capacity of residual liquid. Mechanical property evaluation reveals that the adoption of pressure with 0.2MPa during solidification generates significant improvement of tensile strength, which gives a promising method for the production of high performance lightweight magnesium alloy.

A modified Johnson-Cook constitutive relationship for a rare-earth containing magnesium alloy

Lightweight magnesium alloy has recently attracted a considerable interest in the automotive and aerospace industries to improve fuel efficiency and reduce CO2 emissions via the weight reduction of vehicles. Rare-earth (RE) element addition can remarkably improve the mechanical properties of magnesium alloys through weakening crystallographic textures associated with the strong mechanical anisotropy and tension-compression yield asymmetry. While the addition of RE elements sheds some light on the alteration in the mechanical anisotropy, available information on the constitutive relationships used to describe the flow behavior of RE-containing magnesium alloys is limited. To establish such a constitutive relationship, uniaxial compressive deformation tests were first conducted on an extruded Mg-10Gd-3Y-0.5Zr (GW103K) magnesium alloy at the strain rates ranging from 1×10−1 to 1×10−4 s−1 at room temperature. A modified Johnson-Cook constitutive equation based on a recent strain hardening equation was proposed to predict the flow stresses of GW103K alloy. Comparisons between the predicted and experimental results showed that the modified Johnson-Cook constitutive equation was able to predict the flow stresses of the RE-containing magnesium alloy fairly accurately with a standard deviation of about 1.8%.

The Application of Magnesium Alloy in Automotive Seat Design

Vehicle weight reduction has become the development trend of the automotive industry, lightweight magnesium alloy as the material can be applied to automobile parts to achieve more substantial weight loss results. This paper adopts a car seat frame, refer to the regulations for strength of seat system, finite element software ANSYS, the static strength analysis of magnesium alloy seat frame. And further on carbon steel material for static strength analysis, conclusions and magnesium alloys were compared, from lightweight, economy and other aspects show the superiority of magnesium alloys.

Microstructure and Fatigue Properties of a Friction Stir Lap Welded Magnesium Alloy

Friction stir welding (FSW), being an enabling solid-state joining technology, can be suitably applied for the assembly of lightweight magnesium (Mg) alloys. In this investigation, friction stir lap welded (FSLWed) joints of AZ31B-H24 Mg alloy were characterized in terms of the welding defects, microstructure, hardness, and fatigue properties at various combinations of tool rotational rates and welding speeds. It was observed that the hardness decreased from the base metal (BM) to the stir zone (SZ) across the heat-affected zone (HAZ) and thermomechanically affected zone (TMAZ). The lowest value of hardness appeared in the SZ. With increasing tool rotational rate or decreasing welding speed, the average hardness in the SZ decreased owing to increasing grain size, and a Hall–Petch-type relationship was established. Fatigue fracture of the lap welds always occurred at the interface between the SZ and TMAZ on the advancing side where a larger hooking defect was present (in comparison with the retreating side). The welding parameters had a significant influence on the hook height and the subsequent fatigue life. A relatively “cold” weld, conducted at a rotational rate of 1000 rpm and welding speed of 20 mm/s, gave rise to almost complete elimination of the hooking defect, thus considerably (over two orders of magnitude) improving the fatigue life. Fatigue crack propagation was basically characterized by the formation of fatigue striations concomitantly with secondary cracks.

Lap shear strength and fatigue behavior of friction stir spot welded dissimilar magnesium-to-aluminum joints with adhesive

Lightweighting is currently considered as an effective way in improving fuel efficiency and reducing anthropogenic greenhouse gas emissions. The structural applications of lightweight magnesium and aluminum alloys in the aerospace and automotive sectors unavoidably involve welding and joining while guaranteeing the safety and durability of motor vehicles. The objective of this study was to evaluate the lap shear strength and fatigue properties of friction stir spot welded (FSSWed) dissimilar AZ31B-H24 Mg alloy and Al alloy (AA) 5754-O in three combinations, i.e., (top) Al/Mg (bottom), Al/Mg with an adhesive interlayer, and Mg/Al with an adhesive interlayer. For all the dissimilar Mg-to-Al weld combinations, FSSW induced an interfacial layer in the stir zone (SZ) that was composed of intermetallic compounds of Al3Mg2 and Al12Mg17, which led to an increase in hardness. Both Mg/Al and Al/Mg dissimilar adhesive welds had significantly higher lap shear strength, failure energy and fatigue life than the Al/Mg dissimilar weld without adhesive. Two different types of fatigue failure modes were observed. In the Al/Mg adhesive weld, at high cyclic loads nugget pull-out failure occurred due to fatigue crack propagation circumferentially around the nugget. At low cyclic loads, fatigue failure occurred in the bottom Mg sheet due to the stress concentration of the keyhole leading to crack initiation followed by propagation perpendicular to the loading direction. In the Mg/Al adhesive weld, nugget pull-out failure mode was primarily observed at both high and low cyclic loads.

Experimental and numerical investigation of an adaptive simulated annealing technique in optimization of warm tube hydroforming

Simulated annealing technique – which has attracted significant attention as being suitable for combinatorial optimization problems – has been used in many engineering applications. In current research, this method is used in optimization of a complicated forming process. Warm tube hydroforming is a new technology in the forming of lightweight aluminum and magnesium alloys in automotive, electronics and leisure industries. Owing to the complex nature of this process at high temperatures, and difficulty of obtaining the optimized forming conditions, this process has not received the credit it deserves yet. A new method for optimization of the warm tube hydroforming process is developed by using the simulated annealing algorithm with a novel adaptive annealing schedule. The optimal pressure loading paths are obtained for AA6061 aluminum alloy tubes with different wall thicknesses and corner fillets. The results obtained by simulated annealing technique are verified numerically and experimentally.

Microstructure and fatigue properties of Mg-to-steel dissimilar resistance spot welds

The structural application of lightweight magnesium alloys in the automotive industry inevitably involves dissimilar welding with steels and the related durability issues. This study was aimed at evaluating the microstructural change and fatigue resistance of Mg/steel resistance spot welds, in comparison with Mg/Mg welds. The microstructure of Mg/Mg spot welds can be divided into: base metal, heat affected zone and fusion zone (nugget). However, the microstructure of Mg/steel dissimilar spot welds had three different regions along the joined interface: weld brazing, solid-state joining and soldering. The horizontal and vertical Mg hardness profiles of Mg/steel and Mg/Mg welds were similar. Both Mg/steel and Mg/Mg welds were observed to have an equivalent fatigue resistance due to similar crack propagation characteristics and failure mode. Both Mg/steel and Mg/Mg welds failed through thickness in the magnesium sheet under stress-controlled cyclic loading, but fatigue crack initiation of the two types of welds was different. The crack initiation of Mg/Mg welds was occurred due to a combined effect of stress concentration, grain growth in the heat affected zone (HAZ), and the presence of Al-rich phases at HAZ grain boundaries, while the penetration of small amounts of Zn coating into the Mg base metal stemming from the liquid metal induced embrittlement led to crack initiation in the Mg/steel welds.