Cast AZ91D Research Articles

Influence of electric pulse on microstructural characteristics and mechanical properties of cast AZ91D magnesium alloy

The application of high-energy electric pulses has emerged as a promising technique for refining the grain structure, inducing solid phase transformations, and weakening the weave structure of cast AZ91D magnesium alloy, thereby enhancing its rolling performance during molding processes. This study investigates the comparative effects of electric pulse treatment, homogenized annealing, and their combination on the microstructure and mechanical properties of cast AZ91D magnesium alloy under various process conditions. Electric pulse treatment offers several advantages over traditional homogenized annealing methods, including high energy efficiency, reduced processing time, and eco-friendly energy conservation. By avoiding excessive heating and material deformation, this method ensures improved integrity and stability of the material. This study provides an in-depth analysis of how changes in frequency and voltage during electrical pulse processing influence the microstructure and mechanical properties of the alloy. Experimental results reveal that optimal enhancements occur at a pulse frequency of 640 Hz and an output voltage of 240 V, which refine the β-Mg17Al12 phase from a large flaky structure to a fine worm-like form, resulting in significant grain refinement and reduced weaving strength. Consequently, there is a substantial improvement in mechanical properties, with the specimens transitioning from brittle fracture to a mixed brittle-tough fracture mode. Tensile strength and elongation exhibit remarkable enhancements of 51.4 % and 91.7 %, respectively, compared to untreated specimens. Furthermore, the combined application of electric pulse treatment across all three processing conditions consistently yields superior results, while homogenized annealing followed by electric pulse treatment leads to a decline in mechanical properties. These findings highlight the efficacy of electric pulse treatment as a viable method for enhancing the microstructure and mechanical properties of cast AZ91D magnesium alloy, with significant implications for optimizing manufacturing processes in various industries.

SiC actions on characteristics analysis of AZ91D hybrid nanocomposite by liquid state processing

AbstractWith an inherent lowest density and distinct solubility with enhanced mechanical behavior reason, the magnesium alloy composite is extensively used in the auto and aero sectors. The processing of magnesium alloy found micro‐cracks and voids between the oxidation spot, which fails properties. Through the sulfur hexafluoride (SF6) atmosphere, the AZ91D alloy hybrid nanocomposites are synthesized with 10 wt% alumina (Al2O3) and 0, 3, 6, and 9 wt% of silicon carbide (SiC) nanoparticles via a liquid state process with 400 rpm stir speed followed by vacuum die casting. The effect of SiC actions on physical behavior, microstructural formation, and mechanical properties of AZ91D/10 wt%Al2O3, AZ91D/10 wt%Al2O3/3 wt% SiC, AZ91D/10 wt% Al2O3/6 wt% SiC, and AZ91D/10 wt% Al2O3/9 wt% SiC composites are studied and its results compared with cast AZ91D alloy. Due to the actions of SiC in AZ91D/10 wt%Al2O3, the composite density conforms to the rule of mixture, and the void and micro‐cracks are limited (less than 1%) by the impact of the casting process, as evidenced in the microstructural illustration. An effect of 10 wt% Al2O3 and 9 wt% SiC contents in AZ91D facilitates maximum tensile strength of 181 MPa, improved elongation percentage of 2.2%, optimum hardness of 85HV, and superior impact toughness of 21.8 J/mm2, which is higher than the all other compositions.

Effect of Surface Strain to Hydroxide Layer Formation on High-Pressure Die Casting Magnesium Alloy

Magnesium hydroxide layer improve corrosion resistance of magnesium alloys. Nonuniform strain on magnesium alloys surface was reported that affected to layer formation and corrosion resistance properties. Hydroxide layer formed to high pressure die cast ASTM AZ91D magnesium alloy, then investigated to correlation between hydroxide layer formation and residual stress and strain distribution on alloy surface which were measured by X-ray. Strain distribution was evaluated by full width half maximum (FWHM) value. Formed hydroxide layer was well compatible with FWHM distribution in as cast specimen. Heat treated for homogenization was carried out to inspection for correlation FWHM. FWHM was significantly lowering by heat treatment. Hydroxide layer tends to thin where FWHM value was low, therefore correlation between nonuniform strain and hydroxide layer formation was found out.

On the deformation behavior of heterogeneous microstructure and its effect on the mechanical properties of die cast AZ91D magnesium alloy

Both a conventional flow distributer and an improved one with a flow buffer were applied respectively during the high pressure die casting (HPDC) process, and samples of AZ91D magnesium alloy with different microstructure mainly consisting of α-Mg grains, β-phase and porosities were obtained. According to the grain orientation analysis, the predominant deformation behavior in α-Mg grains was dislocation slip, supplemented by deformation twinning. Dislocation slip was more difficult to occur in the samples with the improved flow distributer on account of the fact that the size of α-Mg grains in the microstructure was finer and more uniform. During the in situ tensile deformation test, cracks were observed to initiate from gas-shrinkage pore and island-shrinkage, and two main crack propagation mechanisms, porosity growth and coalescence were found accordingly. When the crack was in contact with the β-phase, it would pass through and fracture the network β-phase, whereas bypass the island β-phase by detaching it from the surrounding α-Mg grains. Mechanical property tests showed that the samples with relatively more homogeneous microstructure would perform higher mechanical properties, which was the combined effect of matrix α-Mg grains, β-phase, and porosities.

The Investigation on Newly Developed of Hydrophobic Coating on Cast AZ91D Magnesium Alloy Under 3.5 wt% NaCl Solutions

The Investigation on Newly Developed of Hydrophobic Coating on Cast AZ91D Magnesium Alloy Under 3.5 wt% NaCl Solutions

Mechanisms of Cracking in Laser Welding of Magnesium Alloy AZ91D

Considerable research has been carried out to study the laser welding of magnesium alloys. However, the studies are mainly devoted to butt welding, and there has been limited information in the published literature concerning the bead-on-plate laser welding of AZ91D, even though bead-on-plate welding is required for the repair of cast AZ91D parts with surface defects. In the present investigation, surface cracking of the weld metal was observed when an AZ91D magnesium alloy was bead-on-plate welded using the laser welding method. This paper presents the experimental results and analyses to show that the cracking is “solidification cracking” initiated from the weld surface under high thermal stresses. This is in contrast to the “liquation cracking” observed in heat affected zones in tungsten inert gas welding of the same magnesium alloy. Laser power was found to be one of the main factors affecting the distance of the crack propagation. The higher laser power resulted in longer crack propagation distance into the weld metal. It is demonstrated that hot cracking could be avoided by lowering the laser power and welding speed.

Influence of Ni interlayer on interfacial microstructure and mechanical properties of Ti-6Al-4V/AZ91D bimetals fabricated by a solid–liquid compound casting process

Abstract The solid–liquid compound casting of Mg-AZ91D and Ti-TC4 alloys was developed by using pure Ni electro-deposited coating. The pouring temperatures of 660 ℃, 690 ℃, 720 ℃ and 750 ℃ were chosen to investigated the effects of casting temperatures on microstructural evolution, properties, and fracture behaviors of Ni-coated TC4/AZ91D bimetals by the solid–liquid compound casting (SLCC). The scanning electron microscopy (SEM) and the energy dispersive spectroscopy (EDS) results showed that the interfacial zone mainly composed of nickel, Mg2Ni and Mg-Al-Ni in the bimetals cast at 660 ℃. As the pouring temperature was increased to 750 ℃, the width of the interface zone, which mainly composed of δ(Mg), Mg2Ni, Mg-Al-Ni, Mg3TiNi2 and Al3Ni, gradually increased. The microhardness tests showed that the micro-hardness of the interface zone was smaller than that of TC4 substrate but larger than that of the cast AZ91D matrix. At the pouring temperature of 720 ℃, the Ni-coated TC4/AZ91D bimetals had the most typical homogeneous interface, which had granular Mg-Al-Ni ternary phase but no ribbon-like Al3Ni binary phase, and achieved the highest shear strength of 97.35 Mpa. Meanwhile, further fracture behavior analysis showed that most fracture failure of Ni-coated TC4/AZ91D bimetals occurred at the Mg2Ni + δ(Mg) eutectic structure and Al3Ni hard intermetallic.

Effect of Process Parameters on Distortion and Residual Stress in High-Pressure Die Cast AZ91D Components After Clean Blasting and Painting

A high-pressure die-casting process was employed to produce AZ91D components. These cast components were exposed to three different post-treatments: (1) clean blasting, (2) clean blasting and painting, and (3) painting (without clean blasting). The influence of the process parameters first phase injection speed, temperature of fixed half of the die, cooling time, and intensification pressure on distortion and residual stress of the components after each post-treatment were investigated. The results showed that intensification pressure was the most significant factor among the four parameters.

Al8Mn5 in High-Pressure Die Cast AZ91: Twinning, Morphology and Size Distributions

Manganese-bearing intermetallic compounds (IMCs) are important for limiting micro-galvanic corrosion of magnesium-aluminum alloys and can initiate cracks under tensile load. Here, we use electron backscatter diffraction (EBSD), deep etching, and focussed ion beam (FIB) tomography to investigate the types of Al-Mn phases present, their faceted growth crystallography, and their three-dimensional distribution at different locations in high-pressure die cast (HPDC) AZ91D. The Al-Mn particle size distributions were well-described by lognormal distributions but with an additional population of externally solidified crystals (ESCs) formed in the shot chamber analogous to α-Mg ESCs. The large Al8Mn5 particles were cyclic twinned. Differences in the particle size distributions and number density in the center compared with the HPDC skin are identified, and the spatial relationship between Mg17Al12 and Al-Mn particles is explored.

Experimental study on the fracture behavior of AZ91D magnesium alloy under complex loading

In this study, quasi-static compression, tensile, shear, and combined compression-shear tests are conducted on cast AZ91D magnesium (Mg) alloy to study its fracture behavior. Shear-compression specimens are applied instead of complex loading device to obtained the fracture response of Mg alloy under mixed compression/shear tests. Results show that the stress states of specimens can be controlled by changing the loading angle. The strength differential effect is observed, and the criterion with von Mises form cannot give an appropriate description of the fracture behavior of Mg alloy for its dependence on the direction of normal stress. The criterion with the form of odd function and that contains two deviatoric stress invariants is utilized to describe the fracture behavior of Mg alloy. In addition, the effect of pressure term and the direction of normal stress on the fracture strength of Mg alloy are commonly mistaken for the other, and the detailed method to distinguish these two effects has been conducted on the basis of the criteria of f =(J2,J3) and f =(I1,J2,J3).

Effect of mechanical vibration on microstructure and properties of cast AZ91D alloy

Abstract The effects of mechanical vibration frequency and amplitude on solidification filling, microstructure and mechanical properties of cast AZ91D alloy were studied. The results show that when the mechanical vibration frequency of 100 Hz and the mechanical amplitude of 1.0 mm, the solidification filling capacity of AZ91D alloy is the best; the length, width and aspect ratio of the β-Mg17Al12 in AZ91D alloy decrease first and then increase with the increase of mechanical vibration frequency, and gradually decrease with the increase of mechanical amplitude, the minimum value was obtained when the mechanical vibration frequency of 100 Hz and the mechanical amplitude of 1.0 mm. At this time, the tensile strength and yield strength of cast AZ91D alloy are 143.4 MPa and 121.6 MPa, respectively, which are the suitable mechanical vibration parameters for cast AZ91D alloy.

Optimization of AZ91D Process and Corrosion Resistance Using Wire Arc Additive Manufacturing

Progress on Additive Manufacturing (AM) techniques focusing on ceramics and polymers evolves, as metals continue to be a challenging material to manipulate when fabricating products. Current methods, such as Selective Laser Sintering (SLS) and Electron Beam Melting (EBM), face many intrinsic limitations due to the nature of their processes. Material selection, elevated cost, and low deposition rates are some of the barriers to consider when one of these methods is to be used for the fabrication of engineering products. The research presented demonstrates the use of a Wire and Arc Additive Manufacturing (WAAM) system for the creation of metallic specimens. This project explored the feasibility of fabricating elements made from magnesium alloys with the potential to be used in biomedical applications. It is known that the elastic modulus of magnesium closely approximates that of natural bone than other metals. Thus, stress shielding phenomena can be reduced. Furthermore, the decomposition of magnesium shows no harm inside the human body since it is an essential element in the body and its decomposition products can be easily excreted through the urine. By alloying magnesium with aluminum and zinc, or rare earths such as yttrium, neodymium, cerium, and dysprosium, the structural integrity of specimens inside the human body can be assured. However, the in vivo corrosion rates of these products can be accelerated by the presence of impurities, voids, or segregation created during the manufacturing process. Fast corrosion rates would produce improper healing, which, in turn, involve subsequent surgical intervention. However, in this study, it has been proven that magnesium alloy AZ91D produced by WAAM has higher corrosion resistance than the cast AZ91D. Due to its structure, which has porosity or cracking only at the surface of the individual printed lines, the central sections present a void-less structure composed by an HCP magnesium matrix and a high density of well dispersed aluminum-zinc rich precipitates. Also, specimens created under different conditions have been analyzed in the macroscale and microscale to determine the parameters that yield the best visual and microstructural results.

Correlation between Density and Microstructural Features in Vacuum Die Cast AZ91D Magnesium Alloy

Correlation between Density and Microstructural Features in Vacuum Die Cast AZ91D Magnesium Alloy

High Temperature Strength and Stress Relaxation Behavior of Dilute Binary Mg Alloys

Monotonic compression and stress relaxation tests were carried out on specimens of 6 cast binary alloys with (at. pct) 2.5 Al, 0.6 Sn, 2.2 Zn, 0.9 Nd, 0.8 Gd and 1.3 Y, and of a similarly cast AZ91D alloy for reference. The solute concentration of the binary alloys was kept deliberately low to limit precipitation hardening effects during the testing, done in the solution heat treated and quenched condition. Compression testing was carried out at 298 K, 373 K and 453 K (25 °C, 100 °C and 180 °C) for all of the alloys and at 493 K and 523 K (220 °C and 250 °C) for the Nd-, Gd- and Y- containing ones. Stress relaxation was done at 453 K (180 °C) at either a predetermined strain (0.05) or stress (150 MPa). The Mg-Al and the AZ91 alloys softened considerably above 373 K (100 °C). The rest of the alloys exhibited increasing linear strain hardening in compression and reduced stress relaxation, in the order Sn, Zn, Nd, Gd and Y, an indication of a progressively stable dislocation substructure, hence of an increasingly extended athermal regime in the strength-temperature relationship. The overall strain hardening behavior matches that of commercial alloys involving the same solutes at comparable or higher concentrations, and can be accounted for through the respective tendency of the solute atoms to develop short range order. This tendency is lowest for the near-random solid solution introduced by Al, and highest for Nd, Gd and Y, in agreement with their respective phase diagrams. The implications for creep resistant alloy selection and design are discussed.

Effect of multi-step slow shot speed on microstructure of vacuum die cast AZ91D magnesium alloy

Two multi-step (two-step and three-step) slow shot speeds were used in the vacuum die casting process of AZ91D magnesium alloy. The vacuum pressure variation in the die cavity before mold filling was monitored by using a pressure sensor. The microstructures of the produced castings were analyzed with optical microscope and image analysis software. The experimental results demonstrate that, the vacuum pressure in the die cavity at the beginning of mold filling is significantly reduced by using three-step slow shot speed, resulting in a low gas porosity level in the produced castings. At an appropriate multi-step slow shot speed, the dwell time of the liquid metal in the shot sleeve before mold filling can be reduced and the flow of the liquid metal in the shot sleeve at the later stage of the slow shot process can be restrained, which cause a low externally solidified crystal content in the produced castings.

Vacuum assisted high-pressure die casting of AZ91D magnesium alloy at different slow shot speeds

The effects of vacuum assistance on the microstructure and mechanical properties of high-pressure die cast AZ91D alloy at different slow shot speeds were evaluated. Plate-shaped castings of AZ91D alloy were carried out on a TOYO BD–350V5 cold chamber die casting machine incorporated with a self-improved TOYO vacuum system. It was found that the vacuum pressure in the die cavity at the beginning of mold filling increases with the increase of slow shot speed, following a cubic polynomial curve, resulting in a decline in the porosity-reduction ability of vacuum assistance with the increase of slow shot speed. The externally solidified crystal (ESC) contents in conventional and vacuum die castings behave similar against the slow shot speed. The tensile properties of vacuum die castings were strongly influenced by the ESC content at relative low slow shot speeds. With the increase of slow shot speed, the influence of the gas porosity level in vacuum die castings would get prominent.

Environmental Friendly Conversion Coating Formed on Magnesium Alloys and its Anti-Corrosion Performance

Conversion coatings on cast AZ91D magnesium alloy were prepared in the manganese dihydro phosphate baths. The corrosion behavior of the coated and uncoated alloys has been investigated by polarization curve methods. The morphology and composition of coated surfaces were investigated by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX ) as well as X-ray photoelectron spectroscopy (XPS) techniques. It is found that the conversion coating surface characterized by crystal particle and was composed of Mn3(PO4)2. Electrochemical investigation results indicated that the phosphate conversion coating could enhance the corrosion potential in great extent of about 1300mV compared with Mg alloy substrate.

Effect of Solid Solution Treatment on Fatigue Behavior of Cast Magnesium Alloy

The effects of solid solution treatment on high cycle fatigue behavior of cast magnesium alloy AZ91D were investigated using an up-and-down load method. High cycle fatigue tests were carried out up to 107cycles at a stress ratio R=0.1 and frequency of 90Hz on specimens using a high frequency fatigue machine. The results showed that the fatigue strength of cast AZ91D magnesium alloy increase from 54.5Mpa to 71.5Mpa after solid solution treatment (T4) at 415°C, keeping temperature 16hours. The micro-fatigue fracture surface of alloy included fatigue initiation area, fatigue crack propagation area and fatigue fracture area. Fatigue crack of the alloys initiate principally at inclusions and shrinks under subsurface. The fatigue fracture of test specimens show the rupture characteristics of quasi-cleavage(as-cast alloy) and toughness(T4 alloy), respectively.

Effects of Y on microstructure and property of heat treated AZ91D magnesium alloy prepared by lost foam casting process

As cast AZ91D and AZ91D+1·0 wt-%Y magnesium alloy were prepared by the lost foam casting process and then treated by solution and aging treatment. The effects of Y on the microstructure and mechanical properties of heat treated AZ91D magnesium alloy were investigated. The results show that the addition of Y to AZ91D alloy formed the Al2Y phase, which still existed after solution treatment. During the aging treatment process, the rate of β-Mg17Al12 phase precipitating in AZ91D+1·0 wt-%Y alloy was much slower than in AZ91D alloy because the formation of Al2Y phase led to the depletion of Al atoms. The addition of Y was thus claimed to play a key role in delaying the age hardening peak on AZ91D alloy.

Effects of on-line solution and off-line heat treatment on microstructure and hardness of die-cast AZ91D alloy

The effects of on-line solution, off-line solution and aging heat treatment on the microstructure and hardness of the die-cast AZ91D alloys were investigated. Brinell hardness of die-cast AZ91D alloy increases through on-line solution and off-line aging treatment but decreases after off-line solution treatment. By X-ray diffractometry, optical microscopy, differential thermal analysis, scanning electron microscopy and X-ray energy dispersive spectroscopy, it is found that the microstructures of the die-cast AZ91D magnesium alloy before and after on-line solution and off-line aging are similar, consisting of α-Mg and β-Al12Mg17. The precipitation of Al element is prevented by on-line solution so that the effect of solid solution strengthening is enhanced. The β-Al12Mg17 phases precipitate from supersaturated Mg solid solution after off-line aging treatment, and lead to microstructure refinement of AZ91D alloy, so the effect of precipitation hardening is enhanced. The β-Al12Mg17 phases dissolve in the substructure after off-line solution treatment, which leads to that the grain boundary strengthening phase is reduced significantly and the hardness of die cast AZ91D is reduced.