AM50 Alloy Research Articles

Analysis of local stress/strain fields in an HPDC AM60 plate containing pores with various characteristics

Casting pores are regarded as the main factor causing stress/strain concentrations, facilitating the initiation of microcracks and shortening the plasticity of a cast component. The influence of pore characteristics (i.e., size, morphology, and position) on local stress concentration in a High Pressure Die Cast (HPDC) AM60 sample is studied utilizing X-ray tomography (XRT) and image-based finite element (FE) techniques. Heterogeneous porosity distribution is identified in terms of volume fraction and projected area ratio per segment. Statistically results demonstrate that small pores (volume < 0.01 mm3) have higher number frequency and sphericity. In contrast, large pores (volume > 0.01 mm3) account for a very low number frequency (0.3%), and complex shape. The present study addresses the local stress/strain behavior in a cast-pore containing HPDC AM60 sample during tensile loading investigated using 3D image-based models which consider the actual size, morphology, and spatial distribution of pores based on XRT images and consider the actual material properties of the AM60 alloy. Simulation results show that the local stress/strain around a pore evolves progressively with deformation. The strain at a certain pore location may be amplified or reduced in the presence of other pores, depending on the specific location of the concerning pores. Also, the ratio between the projected area of a pore and its shortest distance to the free surface (PA/SD) could give a good indication of the max local stress concentration around the pore surface. The weakening of Ktpl values of pores found in defect bands are principally due to the pore orientation concerning the load direction. These findings may be extended to provide additional insight into the damage mechanisms in material containing casting pores and to enhance understanding of the ductility variation in terms of local deformation fields around pores and their interactions.

Low-Cost Biobased Coatings for AM60 Magnesium Alloys for Food Contact and Harsh Environment Applications.

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 μm thick white lacquer and a 120 μm 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° and 24 h in hot coffee at 60 °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.

Statistical Optimization of Electromagnetic Stirring Parameters for Semisolid AM60 Slurry Using Taguchi-Based Grey Relational Analysis

In the present study, the effect of electromagnetic stirring parameters, including stirring time, pouring temperature and stirring frequency, on the morphology of the AM60 alloys was investigated using Taguchi-based grey relational analysis (TGRA). Each parameter of the process was analyzed at three levels. To accommodate all parameters, an orthogonal array L9 based on the Taguchi approach was used. The optimum parameters were chosen, using different microstructural responses such as shape factor, roundness, average grain size, average grain density and average aspect ratio. The optimal processing parameters were found to be 240 s, 30 Hz and 610 °C for stirring time, stirring frequency and pouring temperature, respectively. Results showed that the shape factor, roundness and average grain density were improved by 33%, 12.8% and 5.5%, respectively. Moreover, the average grain size and the aspect ratio decreased compared to those related to the preliminary set of experimental parameters, which represents the refining of the primary α-Mg phases. In addition, optimal experiment shows a dramatic improvement in tensile strength, uniform elongation and hardness compared to the initial conditions. Besides, the overall grey relational grade was compared to an initial set of experimental parameters, showing an improvement of 64%.

Finite element analysis of AM30 magnesium alloy sheet in the laser bending process

ABSTRACT In the present work, a fully coupled thermo-mechanical analysis is presented to obtain the desired bend angle in the sheet made of AM30 magnesium alloy. The finite element method (FEM) based software ABAQUS 6.10 is employed to estimate the temperature, stress and strain distribution with time for different laser bending process parameters. An FEM proposed model is validated with the experimental results. Some parametric study has been performed to see the influence of laser process parameters on AM30 alloy. Single and multi-passes laser line heating is employed, and observed that the bend angle achieved in multi-passes is approximately 430% higher than the single pass. Hence, the results presented in this paper can be used to assess the applicability of AM30 magnesium alloy in laser-based forming industries.

Effect of hydroxyapatite (HA) addition on microstructure, corrosion resistance of AZ91D, AJ62 and AM60 alloys

In the present research work, the effect on Hydroxyapatite (HA) on the microstructure, corrosion and cytotoxicity of AZ91D, AJ62 and AM60 alloys has been studied. This research paper emphasized upon synthesis and characterization of commercial AZ91D, AJ62 and AM60 alloys after HA addition in terms of microstructure and corrosion resistance. To abstract it out, HA addition tends to refine the grain size which greatly improves the corrosion resistance by forming protective complex metal hydroxides over the material surface. This phenomenon has been experimentally proved from this research. In conclusion, AZ91D/3HA and AJ62/3HA were identified as potential biomaterials based on their finer grain structure, excellent corrosion resistance and exceptionally non-toxic behaviour applications.

Microstructure, tensile and bending behaviour of the as-cast AM50 alloy modified with different antimony and copper additions

The tensile and bending behaviours of the as-cast AM50 alloy were studied after adding different amounts of Sb/Cu (x = 0, 0.5, 1, 3 and 5 wt-%). The optimum levels of the Ultimate Tensile Strength (UTS) and tensile elongation (El%) values were found by adding 0.5 wt-% Sb and 0.5 wt-% Cu. The Yield Strength (YS) and hardness values improved with further additions of these elements. The tensile and hardness properties were investigated to be associated with microstructural features. With Sb additions, the new Mg3Sb2 intermetallics were formed. Moreover, by adding different Cu additions, three Cu-containing intermetallics were scrutinised by using the X-ray diffraction (XRD), thermodynamic calculations and also scanning electron microscopy (SEM). The formation of the new intermetallics could change the morphology of the β-Mg17Al12 phase and suppress its creation. Moreover, the grain refinement effects were different for each alloying element. Therefore, the grain refinement and the presence of new intermetallics had prominent impacts on the tensile and bending properties of the AM50 alloy. While grain refinement had a more positive effect on the UTS values, the YS and bending properties were chiefly controlled by morphology and size of intermetallics.

Role of Materials Science and Engineering in Metal Additive Manufacturing

Additive Manufacturing or Direct Manufacturing, popularly known as 3D Printing, has become the leading-edge manufacturing technology. Today Metal Additive Manufacturing (MAM) is a reality, not only for prototype fabrication, also for functional parts in all industrial sectors. Design freedom that the AM processes offer has led to design and engineering of new, complex, light-weight structures in all applications. However, in order to realize further and widespread use of metal AM for manufacturing critical components, it is necessary to explore the inherent material freedom in AM. While new metal AM materials are being developed, the role of Materials Science and Engineering (MSE) is becoming more apparent than ever before. This presentation will highlight the increasing role of Materials Science and Engineering in metal AM technologies. This presentation will show the essence of metallurgical principles in realizing full scope of material freedom in metal additive manufacturing. This presentation will demonstrate how fundamental MSE principles can be utilized to develop new materials, optimize metal AM and post processing, and their controls that cannot be achieved by conventional manufacturing methods. The examples with new Aluminum AM alloys will be presented, leading to a path of developing advanced and higher performance products for critical applications.

Localized Atmospheric Corrosion of Magnesium-Aluminum Alloys Produced by Semisolid Casting: A 2D and 3D Investigation

The localized corrosion of the two magnesium-aluminum alloys AM50 and AZ91 produced by a semisolid casting method was investigated under atmospheric corrosion conditions, in the presence of NaCl. Gravimetry confirmed the beneficial effect from ambient levels of carbon dioxide (CO2) in suppressing corrosion through the formation of magnesium hydroxy carbonates. Both 2D and 3D characterization revealed that ambient CO2 has a strong influence on the morphology and rate of localized corrosion. In CO2-free atmosphere, the alloys suffered localized corrosion resulting in clustered and interconnected cavities that extended deep into the material. In contrast, corrosion in the presence of ambient levels of CO2 (400 ppm) resulted in evenly distributed shallow corrosion sites. The results indicate that CO2 neutralizes the cathodic areas resulting in diminished cathodic activity and inhibiting NaCl(aq) droplet coalescence.

Microstructural and Mechanical Characterization of the Yb: YAG Laser Welding of High-Pressure Die-Casting Mg-Al-Mn Magnesium Alloy

In this work, the Yb:YAG laser beam welding of the magnesium alloy AM60 was studied. A laser power of 2 kW and a welding speed of 3.5 m / min give a different welding quality than that obtained by CO2 laser with the same parameters. The metallurgical characterization, by optical microscopy, showed the formation of four distinct zones : base metal (BM), heat affected zone (HAZ), the partially fusion zone (PFZ) and the fusion zone (FZ), due to the thermal effect produced by the laser welding thermal cycle. Their dimensions are quantified. The microstructural examination using scanning electron microscopy showed the presence of fine dendritic structure in the FZ although the use of electron dispersive spectroscopy analysis confirm that an eutectic Mg17Al12 phase are surrounded by α-Mg solid solution in the HAZ. Electron backscattered diffraction technique revealed an important grain refinement in FZ and considerable twining phenomena in HAZ, but no texture. X-ray diffraction technique has been used, full width at half maximum of diffraction peaks is measured; it also confirmed the grain refinement in FZ in comparison to BM and HAZ. Both microhardness and tensile proprieties of the complete weld joint are similar to those of the BM.

Fatigue strength of additively manufactured 316L austenitic stainless steel

The microstructures and mechanical properties of the 316L austenitic stainless steel fabricated using binder jet printing (BJP) and selective laser melting (SLM) were investigated and compared with those of the conventionally manufactured (CM) alloy, with particular emphasis on the unnotched fatigue resistance. Results show that the work hardening behavior, ductility, and fatigue strength (σf) of the BJP specimens, which contain significant amounts of pores, are surprisingly comparable to those of the CM alloy. In contrast, the SLM specimens are considerably stronger, especially in terms of the yield strength, less ductile, and far inferior in terms of σf although the porosity in them is relatively smaller as compared to the BJP specimens. These results are rationalized by recourse to the distinct microstructures in the two additively manufactured alloys, which stem from the different processing conditions experienced by them. The planar slip regime that prevails in the early stages of plastic deformation of the BJP alloys and a combination of other microstructural factors lead to the arrest of small cracks that nucleate at the corners of the pores, both under quasi-static and cyclic loads; as a result, neither ductility nor fatigue strength are adversely affected by the porosity in the BJP alloys. In the SLM alloy, the cellular structure, which enhances the yield strength considerably, is too fine whereas the columnar grains are minimally misoriented and coarse enough to induce any crack deflection or arrest. Implications of these results in terms of possible directions for designing AM alloys with high mechanical performance are discussed.

Poly caprolactone/titanium dioxide nanofiber coating on AM50 alloy for biomedical application

Poly caprolactone (PCL) and Poly caprolactone/TiO2 (PCL/TiO2) composite nanofiber with different weight percentage compositions (2 wt%, 4 wt% and 6 wt%) of TiO2 were prepared and coated over AM50 alloy using electrospinning technique. The surface morphology and elemental composition result confirms that the PCL/TiO2 composite nanofiber fiber were successfully electrospun on the surface of AM50 alloy. The degradation behavior of PCL and PCL/6 wt% TiO2 coated AM50 alloy was studied by immersing in Simulated Body Fluid (SBF) solution. The electrochemical and cell proliferation studies reveals that the cellular behavior of PCL and PCL/6 wt% TiO2 composite nanofiber exhibited good support for cell proliferation with enhanced corrosion resistance of AM50 alloy in SBF solution.

Alloying criteria and investigations on the properties of novel AM series alloy fabricated using stir casting

Abstract Magnesium alloys are being used in different sectors for several applications. The low density and high strength to weight ratio have made them indispensable. However, it is observed that Mg alloys are less preferred for the fabrication of critical and complex parts. The inferior mechanical and corrosive properties, along with high inflammability, limit their usage for several applications. The mechanical and physical properties can be enhanced by varying the weight percentage of alloying elements along with an appropriate process for its development. The paper discusses an approach for selection of the alloying elements and their weight percentage with the help of phase diagrams, vital inputs from past literature and properties of commercially available Mg alloys. The developed AM series alloy (Mg-7 wt%Al-0.9 wt%Mn) has shown improvement in the mechanical properties vis-a-vis the existing AM series alloys. The elastic modulus and hardness were observed 24.3% and 16.21% higher than the maximum values of existing AM alloys. For the development of alloy, a systemized stir casting setup was used, which ensured uniform mixing of alloying elements and essentially played an active role in enhancing the mechanical properties.

The gradient microstructure and deformation heterogeneity in HPDC AM60 alloy

As an important manufacturing process for Mg-alloy components, high pressure die casting (HPDC) has attracted considerable attention. However, the application of magnesium alloy high pressure die castings is limited by variations in the mechanical properties, which can be ascribed to a heterogeneous distribution of microstructure. In this work, the through-thickness distribution of the microstructure features (i.e. grain size, β-phase and porosity) of HPDC AM60 alloy and their effects on the strain heterogeneity and the microhardness variation were carefully investigated. The results show that the HPDC AM60 alloy exhibited a gradient structured microstructure, i.e., two skin layers sandwiching a core layer. The skin was mainly comprised of fine grains (diameter ≤10 μm), whereas the core predominately consisted of externally solidified crystals (ESCs). Furthermore, the skin shows higher number and area fractions of β-Mg17Al12 particles. Heterogeneous through-thickness distribution of microhardness was observed in the as-cast sample, and the skin showed higher the microhardness than the core. β-Phase was the primary factor accounting for heterogeneous distribution of microhardness. In the as-cast sample, strain heterogeneity was measured at strain of 3% using digital image correlation (DIC) method. The strain in the skin regions was homogeneous, whereas significant strain heterogeneity was presented in the core. After T4 treatment, remarkable strain heterogeneity was still observed, indicating that β-phase did not have profound effect on deformation heterogeneity. Strain localized at the interdendritic regions of ESCs and the vicinity of grain boundaries in fine-grained regions, where porosity occurred. This illustrates that porosity was the primary factor inducing strain localization.

A comparative study of experimental and adaptive neuro fuzzy inference system based prediction model of machined AM60 magnesium alloy and its parameter effects

Abstract Today in industrialized nations, the machining cost adds up to over 15% of the estimation of every fabricated item.“ Reason why machined component have been proven as one most significant parts of manufacturing science and technology. Magnesium - Mg and its amalgams are widely used due to their remarkable properties such as low density, excellent machinability and recyclability. It is evident that the magnesium alloys are produced into cast. In the aircraft industry, Magnesium alloys have been recognized as an important material. It is important to choose the most optimum machining parameters to obtain very high quality components. The machining variables are completely subjected to the required quality and the nature of the material which is undergoing machining operation. This paper studies the optimization of outputs, namely surface Roughness - Ra and Material Removal Rate – MRR for input variables, for instance cutting speed – IP1, feed rate – IP2 and depth of cut – IP3 for Magnesium alloy AM60 by employing the computational methodologies ANFIS (Gaussian membership function). Investigational approval trails were directed to approve the ANFIS demonstrate. The anticipated Ra (μm) and MRR (mm3/min) was related with measured data, and the maximum prediction error for surface roughness was 0.001115 & 0.0000399% and minimum prediction error for MRR (mm3/min) was 27.8% & 0.7%, while the average prediction error was 0.000452% &7.7% for Ra and MRR.

Corrosion and microstructure of as-cast magnesium alloy AM60-based hybrid nanocomposite

ABSTRACT Two types of Mg alloy AM60-based composites containing (1) only 7 vol.% Al2O3 Fibre and (2) both 7 vol.% Al2O3 Fibre + 3 vol.% Al2O3 nano-Particle, named 7FC and MHNC-7F3NP, respectively, as well as the unreinforced matrix alloy AM60 were prepared by using the preform-squeeze casting technique. The microstructure of the matrix alloy AM60 characterised by optical microscopy (OM), scanning electron microscopy (SEM) and X-ray energy dispersive spectroscopy (EDS) consisted of primary α-Mg grains, eutectic β-Mg17Al12 phases and Al-Mn intermetallics, of which distribution were different from those in the composites. The reinforcement introduction refined the matrix grain structure of the composites significantly. The corrosion behaviours of the 7FC and MHNC-7F3NP composites and the matrix alloy were investigated by using the potential-dynamic polarisation test in 3.5 wt.% NaCl aqueous solution. Compared with the matrix alloy, the introduction of micron-sized alumina fibres decreased the corrosion resistance of the matrix alloy AM60 considerably due to the presence of excessive interfaces, while the high density of grain boundaries and the absence of noble precipitates such as β-Mg17Al12 phases and Al-Mn intermetallics at the grain boundaries in the composites should also be somewhat responsible for their poor corrosion resistance. The addition of the nano-sized particles led to almost no further reduction in the corrosion resistance of the MHNC-7F3NP.

Influence of trace Ca addition on texture and stretch formability of AM50 magnesium alloy sheet

Abstract The AM50, AM50–0.1Ca, AM50–0.3Ca and AM50–0.5Ca (wt.%) alloys were hot-rolled and their mechanical properties were determined for the purpose of investigating the effect of trace Ca addition on the texture and stretch formability of AM50 alloy. The results show that the addition of trace Ca can effectively modify the basal texture, which is characterized by the split of basal poles deviated from the normal direction (ND) after the hot rolling, while a broad spread of the basal planes toward the transverse direction (TD) after the annealing. Such change of the basal texture is related to the prior formation of massive compression twins and the decrease of the c/a ratio. Erichsen value increases from 2.25 to 4.21 mm with the increase of Ca content. The enhancement of stretch formability is ascribed to the weakened basal texture, which results in the increase of n-value and the decrease of r-value.

Comparison of the effects of isothermal equal channel angular pressing and multi-directional forging on mechanical properties of AM60 magnesium alloy

This study investigates the correlation between the microstructure and the mechanical strength of AM60 magnesium alloy processed by equal channel angular pressing (ECAP) and multi-directional forging (MDF) at a constant temperature of 220 °C. The maximum number of passes was six for both severe plastic deformation (SPD) techniques. The minimum achievable grain size was ~1.9 μm for ECAP while it was only ~2.7 μm for MDF. Despite the monotonous reduction of the grain size, the yield and the ultimate tensile strength values decreased for high equivalent strains which was attributed to the decrease of the dislocation density. The maximum achievable strength was higher for ECAP than that for MDF mainly due to the higher dislocation density. Both ECAP and MDF processing led to an improvement of ductility. Based on the strength results, it is evident that the ECAP process is more effective in improving the mechanical properties of AM60 alloy at 220 °C, compared to the MDF process.

Effects of electron beam manufacturing induced defects on fracture in Inconel 718

The effects of electron beam manufactured (EBM) process-induced defects on local microstructural failure initiation and propagation in IN 718 have been investigated. Predictions for transgranular fracture, based on local cleavage plane stresses, and for intergranular fracture, based on dislocation-grain boundary (GB) interactions and evolving dislocation pileups, were combined with a crystalline dislocation-density plasticity approach to understand the influence of AM process-induced defects, such as porosity, NbC precipitates, and regions of dry powder. High local stresses along the peripheries of pores caused crack nucleation, and mismatches in deformation behavior between NbC precipitates and the surrounding matrix led to local stress gradients that induced crack nucleation and decohesion at precipitate/matrix interfaces. Regions of unmelted powder had significant stress accumulations that initiated failure at low nominal strains. Failure due to high localized stresses near regions of unmelted powder was dominant over precipitate/matrix decohesion and crack nucleation near pore peripheries. Based on the predictions, the mechanical behavior of AM alloys is governed by local dislocation-density evolution near process-induced defects, which preferentially nucleate material failure. Furthermore, interactions between these different defect types can significantly accelerate failure initiation and propagation.

Study of the Morphology and Properties of Biocompatible Ca-P Coatings on Mg Alloy.

Magnesium alloys are considered as potential biomaterials for use in orthopedic implantology. The main barrier to the use of Mg alloys in medicine is their overly fast and irregular degradation in body fluids. The use of protective calcium phosphate coatings to increase the corrosion resistance of Mg alloy (AM50 alloy: 4 wt.% Al, 0.3 wt.% Mn, 0.2 wt.% Zn, rest Mg) was examined in this study. The scientific goal of the study was the assessment of the influence of calcium phosphate layer morphology on the corrosion process in Ringer’s solution. Modification of the coating morphology was obtained by changing the chemical composition of the phosphatizing bath using NaOH (NaAM50 sample) or ZnSO4 (ZnAM50 sample). In practice, a more dense and uniform coating could be obtained by the immersion of AM50 alloy in a solution containing ZnSO4 (ZnAM50 sample). In this study, an adhesion test performed on the ZnAM50 sample indicated that the critical load was 1.35 N. XRD phase analysis confirmed that the obtained coatings included dicalcium phosphate dihydrate (CaHPO4*2H2O). The coatings prepared on the NaAM50 and ZnAM50 samples are effective barriers against the progress of corrosion deeper into the substrate. After 120 h immersion in Ringer’s solution, the volume of the evolved hydrogen was 5.6 mL/cm2 for the NaAM50 and 3.4 mL/cm2 for the ZnAM50 sample.

Optimizing the mechanical properties of friction stir welded dissimilar joint of AM60 and AZ31 alloys by controlling deformation behavior

The special microstructure distribution of the friction stir welded (FSW) Mg alloys joints is usually responsible for the non-uniform deformation and poor mechanical properties. Hence, it was possible to improve the joint mechanical properties by modifying the microstructure. In the present study, two kinds of AM60/AZ31 Mg alloys dissimilar FSW joints with different microstructure were obtained using different rotation rates (800 rpm and 1600 rpm). The results of mechanical tests showed that the tensile strength and elongation of the joint at 1600 rpm were 13.5% and 115% higher than those at 800 rpm, respectively. The microstructure observation indicated that the grain size of various zones in the joint at 1600 rpm was obviously larger than that at 800 rpm, especially at the AM60 side. However, there was no obvious difference in the texture distribution of the two welds. In addition, microstructure observation after fracture showed that there were more twins in AM60 side of the joint with coarse grains. These coarse grains promoted the activation of basal slip and twinning in the regions far away from the nugget zone (NZ) interface. This weakened the strain localization of the joint to some extent. Meanwhile, the coarse grain joint had lower concentration degree of the strain and dislocation near the NZ boundary compared with the fine grain joint. These factors led to better mechanical properties of the joint with coarse grains. This work could provide some guidelines for improving the inhomogeneous deformation behavior of dissimilar Mg alloys FSW joints.