Magnesium Alloys

Laser welding will be  an important welding process for different applications in aerospace , aircraft , automotive, electronics  and other industries, due to its capabilities like minimum heat affected zone, welding of various thicknesses, adoptability to welding of various materials possessing widely varying physical properties like melting point, absorption, reflectivity etc. It utilizes laser source as a non contact heat generation technology to weld different materials so as to achieve welds of high quality narrow width and high penetration depths without the need of filler wires. It may be necessary to understand the effect of process parameters on the weldability of materials for successful welding. Laser welding popularly uses two types of lasers like CO2 and Nd:YAG (neodymium doped yttrium – aluminium – garnet)  with different powers. Nd:YAG lasers are used to weld materials of different thicknesses involving powers upto 5 kW. Whereas, CO2 lasers are used for applications which involve higher powers upto 20 kW. Laser welding allows a direct transition from light energy into heat energy. This technique is involved with the process of laser - matter interaction in which various parameters such as pulse energy, pulse duration, spot size, welding speed, laser power, weld width, penetration depth, reflectivity, absorption coefficient, thermodynamic properties etc. are used for analysis. This paper presents a review of the different parameters including process as well as materials on the weldability of various materials like carbon steels, stainless steels, magnesium alloys, aluminium alloys, refractory materials such as vanadium, titanium, zirconium, tantalum etc. The selection of appropriate parameter for welding of specified material is discussed. The prominent weld defects common to the laser welding such as porosity, oxide inclusions, cracking, loss of alloying elements etc., are discussed as related to the microstructure as well as mechanical properties such as hardness, tensile strength and fatigue strength etc.

The selection of proper material for each application is a critical part in every manufacturing industry. In the field of aerospace and automobile the major requirement is light weight yet strong material which can possess every aspect of design parameters. Magnesium alloy one of the major raw material used in these industries due to its light weight, good thermal conductivity etc. Also Friction stir welding is the joining process that is being used in these industries as it is a solid state joining process. This paper gives a detailed review about Friction Stir welding of Mg alloys. The review period is considered from 2009 to 2015.A detailed review about Friction stir welding of Mg alloys has not been done before in this manner. This review work may be a ready reference for subsequent researchers.

Magnesium and its alloys withsevere plastic deformation
(SPD) techniques are more attractive asstructural parts in many industrial applications because of their advantages. In this paper, the importance of wrought magnesium alloys with their applications to accomplish the essential development of components is reviewed. In addition, the different approaches
of equal channel angular pressing (ECAP)process for refining the grain size to achieve the ultrafine grained material on the bulk metals are discussed. Recent developments in the ECAP process are outlined clearly with their importance to overcome many complexities. Various factors like processing temperature of a specimen, die geometry, ram speed, back pressure and processing routes influencing during ECAP process of wrought magnesium alloys at different conditions such as channel angle and corner or outer arc angle are discussed. Finally, the properties of ECAP processed wrought alloys are outlined for improving the microstructure in structural parts.

X. Wang, X. Gong, K. Chou, Review on powder-bed laser additive manufacturing of Inconel 718 parts, Proc. Inst. Mech. Eng. Part B J. Eng. Manuf. 231 (2017) 1890–1903. doi:10.1177/0954405415619883.

http://journals.sagepub.com/doi/abs/10.1177/0954405415619883?journalCode=pibb

This study presents a thorough literature review on the powder-bed laser additive manufacturing processes such as selective laser melting of Inconel 718 parts. This article first introduces the general aspects of powder-bed laser additive manufacturing and then discusses the unique characteristics and advantages of selective laser melting. The bulk of this study includes extensive discussions of microstructures and mechanical properties, together with the application ranges of Inconel 718 parts fabricated by selective laser melting.

Dr. Fritz J. Hansgirg worked in Japan for five years, including 2.5 years in Konan, Korea (now Hungnam, North Korea). This is a reprint of his April 1945 article (written before WWII ended). In it, Hansgirg discussed the challenges that Korea faced once Japan was defeated.

Orthopedic implants, such as those made of stainless steel, cobalt (Co)-based alloys and titanium (Ti) alloys, are commonly used to stabilize, protect, improve, replace or regenerate damaged musculoskeletal tissues both anatomically and functionally in millions of bone injury patients. The biggest drawback of these metallic biomaterials is their non-degradability in the body environment. Magnesium (Mg) and magnesium-based alloys are a new generation of degradable implant materials that have attracted great attention in the past 10 years. There are several advantages of magnesium-based alloys for orthopedic application over other metallic biomaterials. First, magnesium is an essential element for many biological activities, including enzymatic reactions, the formation of apatite and bone cell adsorption. Second, their mechanical properties, including density, elastic modulus and compressive yield strength, are much closer to those of natural bone, and, therefore, they can avoid the stress-shielding effect. Third, magnesium alloys can eliminate the necessity of a second surgery to remove permanent bone implants. Recent results show that alloying of magnesium with aluminum (Al), zinc (Zn), calcium (Ca), zirconium (Zr), yttrium (Y) and rare-earth elements can significantly improve its corrosion resistance and mechanical strength. This paper reviews and compares the mechanical properties, corrosion resistance and biocompatibility of currently researched magnesium-based alloys for use in medical implant applications.

Typical hexagonal engineering materials, such as magnesium and titanium, deform extensively through shear strains and crystallographic reorientations associated with the nucleation, propagation , and growth of twins. To accurately predict their deformation behavior it is, therefore, critical for constitutive models to incorporate these mechanisms. In this work an integrated approach for modeling the concurrent dislocation mediated plasticity and heterogeneous twinning behavior in hexagonal materials is presented. A dislocation density-based crystal plasticity model is employed to predict the heterogeneous distribution of stress, strain and dislocation activity and is coupled to a phase field model for the description of the nucleation, propagation, and growth of {1012} tensile twins. A stochastic model is used to nucleate twins at grain boundaries, and their subsequent propagation and growth are driven by the GINZBURG-LANDAU relaxation of the system free energy which includes the orientation dependent twin interfacial energy and the elastic strain energy. Application of this novel and fully coupled model to the cases of magnesium single crystal, bicrystal, and polycrystal deformation is shown to demonstrate its predictive capability. Numerical simulations predict, in accordance with experimental observations, twin nucleation at grain boundaries followed by twin propagation into the grain interior and subsequent transverse twin thickening. Through this new combination of modeling approaches it is possible to systematically study the twin induced strain fields, the stress distribution along twin boundaries, and the spatial evolution of dislocation density within twins and parent grains.

MgO/ZnO composite coatings were successfully prepared on AZ91 Mg alloy by plasma electrolytic oxidation (PEO) method using electrolytes containing ZnO nanoparticles (NPs) to extend their biomedical applications. The effect of the concentration of 0 to 4.5 g·L −1 ZnO NPs in phosphate-based electrolyte on the microstructure, composition, physical features, corrosion and biodegradation properties of coatings was investigated. Observing the microstructure through field emission scanning electron microscopy (FESEM) confirmed that ZnO NPs were well up-taken in the coating structure with crater-like morphology and, they were mostly accumulated near the pores. As ZnO NPs concentration increased, more particles were incorporated in the coating; however, porosity, thickness and surface roughness reduced. The evaluation of the electrochemical behavior of specimens using potentiodynamic polarization test revealed that the polarization resistance of the samples increased from 9.26 to 683.2 kΩ·cm 2 by adding 4.5 g·L −1 ZnO NPs. The study of corrosion mechanism by identifying the coating features using electrochemical impedance spectroscopy (EIS) indicated that the compacting of the coating and the difficulty of the penetration path of corrosive ions between the coating layers due to the presence of ZnO NPs had a more dominant effect relative to thickness reduction. Conducting the bioactivity test by immersion of coatings in simulated body fluid (SBF) solution for 14 days showed the higher growth of calcium phosphate layer formed on the sample as the concentration of ZnO NPs increases. In addition, the changes in weight loss and volume of hydrogen evolution were much less, and the mechanism of these changes was presented.

The activation of non-basal slip systems is of high importance for the ductility in hcp Mg and its alloys. In particular, for Mg–Y alloys where a higher activation of pyramidal dislocation slip causes an increased ductility detailed characterization of the activated slip systems is essential to understand and describe plasticity in these alloys. In this study a detailed analysis of the activated dislocations and slip systems via post-mortem TEM and SEM-EBSD based slip band analysis in 3% deformed Mg–3 wt% Y is presented. The analysis reveals a substantial activity of pyramidal ocþa4 dislocations with different Burgers vectors. The obtained dislocation densities and active slip systems are discussed with respect to atomistic simulations of nonbasal dislocations in hcp Mg.

Metals are the backbone of manufacturing owing to their strength and formability. Compared to polymers they have high mass density. There is, however, one exception: magnesium. It has a density of only 1.7 g/cm 3 , making it the lightest structural material, 4.5 times lighter than steels, 1.7 times lighter than aluminum, and even slightly lighter than carbon fibers. Yet, the widespread use of magnesium is hampered by its intrinsic brittleness. While other metallic alloys have multiple dislocation slip systems, enabling their well-known ductility, the hexagonal lattice of magnesium offers insufficient modes of deformation, rendering it intrinsically brittle. We have developed a quantum-mechanically derived treasure map which screens solid solution combinations with electronic bonding, structure and volume descriptors for similarity to the ductile magnesium-rare earth alloys. Using this insight we synthesized a surprisingly simple, compositionally lean, low-cost and industry-compatible new alloy which is over 4 times more ductile and 40% stronger than pure magnesium. The alloy contains 1 wt.% aluminum and 0.1 wt.% calcium, two inexpensive elements which are compatible with downstream recycling constraints. Permanent shape changes of metals are enabled by the motion of line defects that break atomic bonds and create new ones along densely packed lattice directions. These defects are referred to as dislocations and their crystallographic features as slip systems. Each dislocation shears the material by one atomic spacing. The motion of up to one light year of dislocation length per cubic meter (10 16 m/m 3) thus enables macroscopic deformation and forming. Metals are typically used in polycrystalline form with crystal sizes of up to several micrometers. A square meter of auto skin sheet for instance can consist of more than 10 10 crystals. Since individual crystals deform only along specific crystallographic directions, macroscopic shape changes require deformation compatibility among them. Accommodating arbitrary deformations thus requires at least 5 independent deformation systems in each crystal to be active 1. While cubic metallic crystals (e.g. steels, Al-alloys) have a sufficiently high number of independent deformation systems due to their high crystal symmetry, most hexagonal crystals exhibit insufficient independent deformation systems 2, 3. Magnesium and its alloys, as the lightest class of structural metals, have a hexagonal lattice structure. Thus, despite some excellent properties such as low mass density, good castability and efficient recyclability 4 , their wider industrial application is fundamentally impeded by their intrinsic poor room temperature ductility. The lack of room temperature formability is caused by deformation being governed by ¯ {0001} 1120 basal <a> dislocation slip and ¯ ¯ ¯ {1012} 1011 tensile twinning 2, 3, 5–14. Basal <a> slip does not allow accommodation of strain along the crystal c-axis but rather a rotation of the crystal c-axes parallel to the loading direction 2, 9, 14 , leading to the so-called basal texture component 9. Consequently, magnesium fails at low strains, Fig. 1. Strain along the crystal c-axis can only be accommodated by the activation of non-basal slip in hexagonal crystals, i.e. it is crucial for compatible polycrystalline deformation of Mg 2, 6, 12–16. Even if dislocations with a <c + a> Burgers vector are formed they do not prevail in pure Mg: Curtin et al. 15 recently showed by using molecular dynamics simulations that dislocations with non-basal Burgers vectors are not stable but dissociate and relax back onto the basal plane in pure Mg. Manipulation of the activation and stability of dislocations and slip systems is possible through the addition of alloying elements. Specifically, dilute alloying with yttrium and rare earth (RE) elements has been shown to improve the room temperature ductility significantly 4–13. Recent studies by combined transmission electron microscopy

Deformation twinning plays a critical role on improving metals or alloys ductility, especially for hexagonal close-packed materials with low symmetry crystal structure. A rolled Mg alloy was selected as a model system to investigate the extension twinning behaviors and characteristics of parent-twin interactions by nondestructive in situ 3D synchrotron X-ray microbeam diffraction. Besides twinning-detwinning process, the " twinning-like " lattice reorientation process was captured within an individual grain inside a bulk material during the strain reversal. The distributions of parent, twin, and reor-ientated grains and sub-micron level strain variation across the twin boundary are revealed. A theoretical calculation of the lattice strain confirms that the internal strain distribution in parent and twinned grains correlates with the experimental setup, grain orientation of parent, twin, and surrounding grains, as well as the strain path changes. The study suggests a novel deformation mechanism within the hexagonal close-packed structure that cannot be determined from surface-based characterization methods.

An anodizing electrolyte solution composed of zirconium oxide nanoparticles (ZrO2-NPs) was nucleated within CaP compounds dispersed in simulated body fluid (SBF) and was then deposited on an AZ31B magnesium alloy. The anodized bioceramic layer is
intended to significantly improve the surface properties of the magnesium alloy by
increasing the resistance to corrosion and improving biological compatibility. A surface
analysis confirmed the successful deposition of the compounds on the AZ31B magnesium
alloy, the mechanical hardness and the surface roughness of the coated samples were
subsequently investigated. The potentiodynamic polarization obtained during the electrochemical corrosion test indicated that the treated samples had an improved corrosion resistance relative to untreated ones. The in vitro cytotoxicity of the prepared samples was evaluated using an indirect extraction test for human endothelial cells (EA.hy926). The results indicated that none of the coated samples exhibited obvious
cytotoxicity. The anodized samples have good cell viability, corrosion resistance and are therefore considered to be good candidates for use with biodegradable magnesium materials for biomedical applications.

The selection of proper material for each application is a critical part in every manufacturing industry.
In the field of aerospace and automobile the major requirement is light weight yet strong material which
can possess every aspect of design parameters. Magnesium alloy one of the major raw material used in
these industries due to its light weight, good thermal conductivity etc. Also Friction stir welding is the
joining process that is being used in these industries as it is a solid state joining process. This paper
gives a detailed review about Friction Stir welding of Mg alloys. The review period is considered from
2009 to 2015.A detailed review about Friction stir welding of Mg alloys has not been done before in this
manner. This review work may be a ready reference for subsequent researchers.

Lightweighting in ground vehicles is today considered as one of the most effective strategies to improve fuel economy and reduce anthropogenic environment-damaging and climate-changing emissions. Magnesium (Mg) alloy, as a strategic ultra-lightweight metallic material, has recently drawn a considerable interest in the transportation industry to reduce the weight of vehicles due to their high strength-to-weight ratio, dimensional stability, good machinability and recyclability. However, the hexagonal close-packed crystal structure of Mg alloys gives only limited slip systems and develops sharp deformation textures associated with strong mechanical anisotropy and tension-compression yield asymmetry. For the vehicle components subjected to dynamic loading, such asymmetry could exert an unfavorable influence on the material performance. This problem could be conquered through weakening the texture via addition of rare-earth (RE) elements. Thus, a number of RE-containing Mg alloys have recently been developed. To guarantee the structural integrity, durability, and safety of highly loaded structural components, understanding the characteristics and mechanisms of cyclic deformation and fatigue fracture of such RE-Mg alloys is of vital importance. In this review, the available fatigue properties including stress-controlled fatigue strength, strain-controlled cyclic deformation characteristics, and fatigue crack propagation behavior are summarized, along with the microstructural change and crystallographic texture weakening in the RE-containing Mg alloys in different forms (cast, extruded, and heat-treated states), in comparison with those of RE-free Mg alloys.

The relationship between the resulting grain size and the applied working strain rate and temperature for the friction stir processing
in AZ31 Mg is systemically examined. The Zener–Holloman parameter is utilized in rationalizing the relationship. The grain
orientation distribution is also studied using the X-ray diffraction.

Friction stir welding (FSW) between 3 mm thick AA 5052-O aluminum alloy plates was investigated in the present study. Different welded specimens were produced by employing a constant tool traverse speed of 120 mm/min and by varying rotating speeds from 800 to 3000 rpm. The welded joints were characterized by its appearances, microstructural and mechanical properties at room temperature. The measurement of different forces acted on the tool during the FSW of AA 5052-O plates provided a significant insight to determine the quality of the welded joints. From the appearances of the welded joints it was evident that, except the tool rotational speed of 3000 rpm all other rotational speeds produced sound welded joints with smooth surface. The joint produced at 1000 rpm yielded a maximum tensile strength of 132 MPa which was 74% of the base material strength. Field emission scanning electron microscopy (FESEM) and energy dispersive spectroscopy (EDS) analyses on the stir zone suggested that, beta-Mg2Al3 intermetallic phases of the base material were mechanically fractured, smeared and mixed to different geometries due to tool stirring. The dissolution and redistribution of beta-Mg2Al3 second phase particles in the stir zone had a considerable effect on the reduction of the tensile strength of the welded joints. The reduction in hardness at the nugget zone (NZ) of the welded joints under different tool rotational speeds could be attributed to the dislocation of Mg-rich phases and segregation of Mg solute atoms at grain boundaries, which drew solute Mg atoms away from the alpha-aluminum matrix. (C) 2014 Elsevier Ltd. All rights reserved.

http://www.sciencedirect.com/science/article/pii/S0261306914008310 
http://eprints.um.edu.my/11621/ 
http://repository.um.edu.my/94959/1/FSW.pdf

The use of magnesium, which is the latest metal of our age, is increasing in parallel with the advances in industry and
technology. Due to its lightness, durability and long life, its usage is increasing in the automotive and space-craft industries.
As a result of the advances in magnesium use, there are innovations in welding methods as well. The desired mechanical
properties can’t be obtained after welding. While there are some difficulties in fusion welding of magnesium material and its
alloys, some of them can’t be joined by fusion welding at all. Weldability of a material is the property that plays an
important role in enabling its wider use and determines the method of producing products out of this material. Magnesium
plates were joined successfully by friction stir welding method. Welded joints are exposed to various mechanic stresses and
especially to dynamic loads. Cracks are observed to occur due to dynamic loads. Plates were joined in butt position and the
mechanical properties of the occurring joint are examined.

Surface-dependent mechanical and corrosion resistance has been enhanced by electroless nickel (EN) deposition on laser surface treated (LST) AZ91D substrate (AZ91D/LST/EN). This proposed method enhanced the surface properties in a better way than conventional LST on EN deposited AZ91D substrate (AZ91D/EN/LST). Microhardness, drysliding wear and electrochemical polarization tests were used to study the hardness, wear and corrosion resistance of these modified surfaces and followed by microstructure, phase composition analysis. The conventional, AZ91D/EN/LST samples produced a relatively smooth, crack-free and hard layer consisting of Ni-Mg intermetallic particles; thereby offered a significant increase in hardness and wear resistance and shortcoming of this method is its significant decrease in corrosion resistance, due to the diffusion of Mg into re-melted layer and the formation of Ni-Mg intermetallic phases. On the other hand, this proposed method AZ91D/LST/EN samples produced an increase in surface hardness and wear resistance and maintains a similar and high corrosion resistance.

The present study deals with the recrystallization behavior of homogenized AZ81 magnesium alloy with emphasizing on the role of mechanical twins and g precipitates. Towards this end a set of hot compression tests were conducted in the temperature range of 250-450 1C under strain rates of 0.003, 0.03 and 0.3 s À 1. The results indicate that the dynamic recrystallization (DRX) has been occurring in the large scales thereby considered as the main factor affecting the related flow stress characteristics. The twin related dynamic recrystallization (including DRX within twin bands and DRX at twin-twin intersections) possesses a great contribution to the formation of new recrystallized grains. The obtained results also confirm that the dynamic precipitation of g phase has a significant effect on hindering the growth of new DRX grains thereby resulting in an outstanding grain refinement. The role of mechanical twinning and dynamic precipitation on the DRX behavior of the alloy is more pronounced at higher and lower Zener-Hollomon parameter, respectively.

The I1 intrinsic stacking fault energy (I1 SFE) serves as an alloy design parameter for ductilizing Mg alloys. In view of this effect we
have conducted quantum–mechanical calculations for Mg15X solid-solution crystals (X = Dy, Er, Gd, Ho, Lu, Sc, Tb, Tm, Nd, Pr, Be, Ti, Zr, Zn, Tc, Re, Co, Ru, Os, Tl). We find that Y, Sc and all studied lanthanides reduce the I1 SFE and render hexagonal closed-packed (hcp) and double hcp phases thermodynamically, structurally and elastically similar. Synthesis, experimental testing and characterization of some of the predicted key alloys (Mg–3Ho, Mg–3Er, Mg–3Tb, Mg–3Dy) indeed confirm reduced I1 SFEs and significantly improved room-temperature ductility by up to 4–5 times relative to pure Mg, a finding that is attributed to the higher activity of non-basal dislocation slip.