Cast Magnesium Alloy Research Articles

Correlation of 3D defect-band morphologies and mechanical properties in high pressure die casting magnesium alloy

For understanding the processing-microstructure-properties correlation of high pressure die casting (HPDC) AZ91D alloy, 3D reconstruction was carried out to characterize the microstructural morphologies of castings produced by four designed HPDC processes. The influence of different parameters (vacuum, slow-shot speed, fast-shot speed) on porosity volume and morphology, defect band width and average externally solidified crystals (ESCs) size of castings were systematically studied. Microstructural characterization revealed that the defect band width was strongly related with the size and quantity of ESCs, rather than the porosity volume. Meanwhile, ESCs were mainly influenced by the slow-shot speed in shot sleeve (ESCs growth time) and fast-shot speed into the die cavity (shear stress of melt flow). Tensile fracture revealed that cracks easily propagated within the defect bands due to the accumulated ESCs and connected irregular pores, while the cracks were restrained in center zone. The mechanical properties of HPDC castings was inversely proportional to the defect band width, and is not dependent on the average volume fraction porosity.

Determination of interfacial heat transfer coefficients for squeeze casting of magnesium alloy AZ91 with various section thicknesses

ABSTRACT In the present work, a step die was made by P20 steel for squeeze casting magnesium alloy AZ91 with five different section thicknesses of 2, 4, 8, 12, and 20 mm under an applied pressure of 60MPa. K-type thermocouples were utilised to measure temperatures of the squeeze casting surfaces as well as three different depths, i.e., 2, 4, and 8 mm from the mould inner wall at each step. With the temperature measurements, interfacial heat transfer coefficients (IHTC) at the casting and mould inner surface and heat fluxes were determined by solving one-dimensional heat conduction formulae using the inverse method. The results of the calculated IHTCs showed that, upon the commencement of squeeze casting, the IHTC values for all the five steps rose very rapidly. Before decreasing, the IHTC at each step reached its own individual peaks. As the section step thickness changed from 2 mm (step 1) to 20 mm (step 5), the IHTC peak values increased significantly. It took comparatively longer time for a thicker step to reach its peak IHTC value, and also to descend its IHTC to a low and steady level.

Optimization of Process Parameters during Pressure Die Casting of A380: a Silicon-Based Aluminium Alloy Using GA & Fuzzy Methodology

Pressure die-casting is generally useful in casting of zinc, Aluminium, magnesium, lead and tin-based alloys. Better surface finish, tolerances and dimensional accuracy can be achieved by optimization of significant process parameters of Pressure die casting (PDC) such as solidifying-time, melting-temperature, fill-up-time, inoculation-pressure and plunger-velocity etc. In addition, with the proper selection of optimum process parameters the PDC defects such as flash, cold-shut, porosity, misrun, etc. also minimized. In the present work, minimization of the PDC defects using artificial intelligent technique comprises of Genetic-algorithm (GA) and fuzzy-logic-methodology (FLM). A380: A silicon based aluminium alloy carburetor-housing is considered for the same. L18 orthogonal array based Taguchi design approach is considered for number of % defects per batch in a lot of 500 components as FLM knowledge base. To estimate the extent of accuracy of predictions made by FLM, regression analysis isperformed. FLM is also validated with R-square approach. Besides this, ANOVA has also been applied to estimate the significance level in terms of percent contribution among the input parameters and defects during PDC. Solidifying-time & fill-up-time has been found most sensitive parameter. Melting-temperature, plunger-velocity and inoculation-pressure are also identified as influencing parameters with comparatively low percent contribution. To optimize process parameters GA is applied and the fitness value is calculated using FLM. From this combination of artificial intelligent approach an optimum combination of process parameter has been obtained. Further, the results are compared with the Taguchi methodology and the approach provides appreciable amount of decrease in PDC-defects by fine tuning the input parameter.

Surface Properties Enhancement of Light Alloys by Appliance of Laser Treatment

Laser surface treatment is at present one of up-to-date methods for surface layer engineering, in this technique into the matrix material are introduced some amount of alloying additives. So the surface layer is obtained in form of composite material consisting of ceramic particle powders with different properties influencing the surface layer appliance possibilities. Using the technology it is possible to obtain a layer revealing a structured structure consisting of the heat affected zone (HAZ), transition zone (TZ) and remelted zone (RZ), as well as the substrate material. The laser is without cracks and defects as well as has with a slightly higher hardness value compared to the raw substrate material. The used laser power range is set in the range between 1.0 to 2.5 Kw, with the laser scan rate of the beam head in a range between 0.25-0.75 m/min, depending of the applied laser power and material used for alloying.This study was conducted to determine the effect of carbide on oxide ceramic powders addition on the microstructure and mechanical properties their changes and enhancement possibilities during a rapid solidification process of the remelted surface layer. The investigation should help to use this laser treatment technology for alloying of ceramic powder particles into the surface of light alloys, especially magnesium and aluminium. The scientific reason of this work is the usage of High Power Diode Laser (HPDL) for improvement of aluminium`s mechanical properties, especially the surface hardness and war resistance.There was found during the investigations and analysis of the results that, the obtained surface layer is without cracks and defects as well as with a relatively higher hardness compared to the raw material, after standard heat treatment. The hardness value increases according to the laser power used so that the highest power applied gives the highest hardness value in the remelted layer, similar relation can be found in the wear resistance parameters, which increases also with increasing laser power.The findings of the investigations allows to state, that the distribution of the used ceramic particles is generally satisfied, especially the carbide powder was confirmed in the alloys matrix, the particles are mainly present in the upper part of the surface layer or in the bottom zone of the remelted area. The hardness value increases in general according to the laser power used and the highest power results with the highest hardness value in the surface layer. The main aim of this work is to investigate and determine the effect of HPDL remelting and alloying on the cast Al-Si-Cu and Mg-Al-Cu cast aluminium and cast magnesium alloys micro structure for possible application in real working conditions mainly for light metal constructions as well as in many branches of the industry like automotive and rail transportation.

Effect of Modification on Microstructure and Properties of AZ91 Magnesium Alloy

Refinement of α-Mg solid solution grains has a significant influence on the improvement of mechanical properties of cast magnesium alloys. In the article, the effects of three modifiers on microstructure and properties of AZ91 magnesium alloy casted to a sand mould were described. Overheating, hexachloroethane and wax-CaF2-carbon powder were applied. The research procedure comprised microstructure analysis by means of light microscopy, scanning electron microscopy and quantitative analysis with AnalySIS Pro® software and mechanical properties’ investigation. The microstructure of AZ91 alloy in the as-cast condition consists of α-Mg solid solution with precipitates of Mg17Al12, Mg2Si and Al8Mn5 phases. It was reported that all applied modifiers cause refinement of α-Mg solid solution grains and a decrease of the volume fraction of α-Mg+Mg17Al12 compound discontinuous precipitates. The best results were obtained in the case of wax-CaF2-carbon powder.

Comparative study on performance and microstructure of composite water-soluble salt core material for manufacturing hollow zinc alloy castings

The water-soluble salt core material has been successfully used for manufacturing hollow aluminum and magnesium alloy castings. However, there is rare report about the water-soluble salt core being used for lower melting point and higher density hollow zinc alloy castings. In order to obtain a high-performance composite water-soluble salt core material (CWSSC) which is suitable for manufacturing hollow-structure zinc alloy castings via high pressure die casting process, the comparative study on performance and microstructure of the salt cores fabricated by gravity casting technology was investigated using KNO3 and KCl as the base salt material with the reinforcements of bauxite or glass-fiber powder. The results show that CWSSC strengthened by reinforcements possesses many advantages of good surface quality and water-solubility rate, high bending strength and impact toughness, low shrinkage and moisture-absorption rate, and CWSSC composed of KNO3-20 mol% KCl with 15 wt% bauxite powder and 15 wt% glass-fiber powder has the better comprehensive performance, whose surface roughness is 0.4758 μm, bending strength is 46.6 MPa, impact toughness is 21.72 kJ/m2, and water-solubility rate is 178.21 kg/(min·m2) in still water at 80 °C with relatively low shrinkage and 24 h moisture-absorption rate. The scanning electron microscope analysis shows that the strengthening-toughening mechanisms of CWSSC mainly include refinement of the grain and deflection of the crack caused by KCl dendritic crystal and the rigid enhanced powders. A practical casting test has been conducted to prove that the developed CWSSC can be used to manufacture hollow-structure zinc alloy castings.

Finite Element Analysis of Extrusion Process for Magnesium Alloy Internal Threads with Electromagnetic Induction-Assisted Heating and Thread Performance Research.

The casting magnesium alloy AZ91D cannot be extruded at room temperature. This paper presents a process for extruding internal threads using AZ91D heated by electromagnetic induction. The feasibility of the process is verified by finite element simulation and experiments. Using DEFORM-3D to simulate the process of extruding a M12 × 1.25 mm threaded hole by electromagnetic induction-assisted heating, the equivalent stress-strain and material flow law in the process of thread deformation was analyzed and verified by experiments. Three parameters—hole diameter, machine speed and heating temperature—were considered to study the influence of different process conditions on the forming torque. The results show that a heating temperature above 523 K can improve the plasticity of AZ91D. The hole diameter has an important influence on the forming torque. The forming process is not suitable for high-speed machining. The surface metal of the thread formed by this process has a strong deformation layer, which can improve the strength and hardness of the thread.

Structure and Mechanical Properties of the CO2 Laser Welded Joint of AZ91 Cast Magnesium Alloy

Structure and Mechanical Properties of the CO2 Laser Welded Joint of AZ91 Cast Magnesium Alloy

Casting of High Aluminum Content AM Series Magnesium Alloys by Using a Horizontal Twin Roll Caster

In this paper, twin roll casting of magnesium alloys with high aluminum content such as, Mg-11 mass%Al-0.2 mass%Mn, Mg-12 mass%Al-0.2 mass%Mn, Mg-13 mass%Al-0.2 mass% have been performed for the purpose of use as an original material for hot forging. Also the mechanical properties of the cast materials were examined. A 10 miri-meters thick strip was cast by the use of a horizontal twin roll caster. The microscopic observation was conducted to investigate into the precipitation of the metal compounds such as Mg17Al12, and the Vickers hardness of the cast strips test were performed. From the result of the roll casting experiments, a 10 mm thick strip was continuously cast at a roll speed of 3.1 m/min. The average grain size of the casting strips was about 46 micron meters. When the aluminum content was 13%, the hardness of the twin roll cast (TRC) strips became 1.7 times higher than that of extruded AZ 31. Also, a uniaxial compression test at elevated temperature was conducted to obtain a true strain-true stress curve for examining possibility of direct hot forging (DHF) of TRC magnesium alloys with high aluminum content.

Role of Matrix Microstructure in Governing the Mechanical Behavior and Corrosion Response of Two Magnesium Alloy Metal Matrix Composites

The microstructure, mechanical properties, and corrosion resistance of two popular magnesium cast alloys, namely Mg–Al–Mn alloy (AM100) and Mg–Zn–Cu alloy (ZC63), and their saffil alumina short-fiber-reinforced composites have been investigated. The results reveal that the mechanical behavior of the magnesium alloy metal matrix composites (Mg-MMCs) was influenced by the nature of the base matrix and the microstructural phases present. The behavior of the composites also depended on the fiber volume fraction. The composites of the two alloys showed an improvement in tensile strength at high temperatures compared with the unreinforced counterpart. Under impact loading and salt spray corrosion conditions, the composites exhibited observable degradation in properties. Under corrosion, the distribution of microstructural phases essentially determined the corrosion resistance of the matrix. The effect of the inherent nature of the alloy matrix in controlling both the mechanical properties and corrosion behavior of the Mg-MMCs is thoroughly discussed.

Effect of wiper on thermal stresses during direct chill casting of magnesium alloy

Understanding the thermomechanical behaviour of an alloy during the Direct Chill (DC) casting process is essential to alleviate the defects in the casting. In this work, conventional direct chill casting process is numerically modelled for evaluating the thermal stress profiles in the casting of AZ31 magnesium alloy. A cooling strategy is used where a wiper is positioned below the mold to reduce the cooling intensity and magnitude of thermal stresses. In this work, the effect of the wiper on the reduction of thermal stress is analysed in detail during the DC casting of AZ31 magnesium alloy. A 2-D computational domain growing along with the casting speed is used to replicate the DC casting process. The temperature and stress profiles are calculated by sequentially solving the energy and momentum balance using the Finite Element Method. The effect of a cooling strategy, on the variation of radial, axial and circumferential stresses is analysed. It is observed that there is a decrease in the circumferential and radial stresses developed in the billet below the mold. Implementation of wiper resulted in higher temperature billet surface which led to reduction of the stresses both in the circumferential and radial direction.

Latest research advances on magnesium and magnesium alloys worldwide

In the past two years, significant progresses have been achieved in high-performance cast and wrought magnesium and magnesium alloys, magnesium-based composites, advanced cast technologies, advanced processing technologies, and functional magnesium materials, such as Mg ion batteries, hydrogen storage Mg materials, bio-magnesium alloys, etc. Great contributions to the development of new magnesium alloys and their processing technologies have been made by Chongqing University, Shanghai Jiaotong University, Chinese Academy of Sciences, Helmholtz Zentrum Geesthacht, Queensland University, Brunel University, etc. This review paper is aimed to summarize the latest important advances in cast magnesium alloys, wrought magnesium alloys and functional magnesium materials worldwide in 2018–2019, including both the development of new materials and the innovation of their processing technologies. Based on the issues and challenges identified here, some future research directions are suggested, including further development of high-performance magnesium alloys having high strength and superior plasticity together with high corrosion resistance and low cost, and fundamental research on the phase diagram, diffusion, precipitation, etc., as well as the development of advanced welding and joining technology.

Effect of melting method on the bio-corrosion resistance of Mg67Zn28Ca5 cast magnesium alloy in simulated body fluid

In recent years, biodegradable magnesium alloys have attracted considerable attention in medical devices, such as permanent implants and stents. However, poor corrosion resistance is a major problem limiting the practical application of magnesium alloys. In this study, Mg67Zn28Ca5 alloys were prepared via two different methods, namely, vacuum induction melting and ulfur hexafluoride shielded melting. The effect of melting method on the bio-corrosion resistance of MgZnCa cast magnesium alloy was also studied. The microstructure and phase composition of Mg67Zn28Ca5 alloys were investigated by optical microscopy and X-ray diffraction. The element distribution and surface morphology of Mg67Zn28Ca5 alloys were examined by scanning electron microscopy and energy-dispersive spectroscopy. The corrosion resistance of Mg67Zn28Ca5 alloys was measured via electrochemical and immersion tests. Results showed uniform composition of the Mg67Zn28Ca5 alloy melted by vacuum induction. Immersed in the simulated body fluid, the corrosion rate of Mg67Zn28Ca5 by vacuum induction melting (0.2618 mm/a) was lower than that by ulfur hexafluoride shielded melting (0.9686 mm/a); the corrosion potential of Mg67Zn28Ca5 melted by vacuum induction (−1313 mV) was nobler than that by ulfur hexafluoride shielded melting (−1483 mV); the corrosion current of Mg67Zn28Ca5 by vacuum induction melting (1.202 × 10−5 A) was lower than that by ulfur hexafluoride shielded melting (4.332 × 10−5 A). The Mg67Zn28Ca5 by vacuum induction melting showed uniform corrosion behavior.

Investigation on reactive wetting during investment casting of magnesium alloy AZ91

During investment casting of Magnesium alloys, the melt contacts with ceramic mould after pouring. The surface quality of the casting is directly affected by the wettability between the melt and ceramic mould material as the Mg melt is reactive to oxygen and moulds are mainly made of ceramic oxides. As the melt wets the wall of ceramic mould, the melt can infiltrate into ceramic mould through the capillaries on the mould surface and then metal can penetrate in the mould that may results in poor surface finish on the surface of the casting. When the temperature of casting and alloy composition fulfill the thermodynamic conditions of interfacial reaction, reaction occurs between melted metal and ceramic materials, leading to development of reactive layers on the surface of casting and deteriorating the surface quality of the casting. Therefore, there is great interest in the industry to minimize or elimination of interface reaction. Ceramic oxides with higher thermal stability found to resist the reactions to some extent. Use of protective gas also helps to overcome the reaction. Wettability has significant effect on the resultant interfacial properties of casting at high temperature liquid metal/solid ceramic systems. The present research focused on mould materials and mould development for suppression of mould-metal reaction in investment castings of magnesium alloy AZ91. An attempt was made to evaluate wetting kinetics for two different mould materials which are Zircon Flour and Fused Alumina. XRD analysis was done on the surface of Mg AZ91 and mould material to find the reaction products for the casting with both mould materials. Fused Alumina was found more suitable over conventional zircon flour for suppressing reaction based on the contact angle and surface roughness.

A Minuscule Appraise on the Outcome of BI and SB Metallic Additives on Refining the Microstructure and Mechanical Behavior of few Magnesium Alloys

This paper reviews the outcome of bismuth and antimony trappings on the microstructure and mechanical behavior of an assortment of commercial magnesium alloys. Various compositions of the Bi and Sb were discussed along with/without combination of other alloying elements. These additions have revealed to be resulted in the formation of Mg3Bi2, Mg3Sb2 intermediate phases when added upon with corresponding alloying elements. Moreover the reasons for the observed changes due to the addition of these alloying elements were also reviewed. It is found that the accumulation of Bi phase as well as intermetallics and Sb intermediates has greatly improved the microstructure belonging to the as cast magnesium alloys thereby improving both mechanical and thermo-mechanical properties. It is also observed in the review that addition of thesealloying elements acted as grain refiner and improved the corrosion resistance of commercial magnesium alloys.

Characterization of the corrosion performances of as‐cast Mg–Al and Mg–Zn magnesium alloys with microarc oxidation coatings

AbstractIn the present study, corrosion‐protective microarc oxidation (MAO) coatings were prepared on AZ31B, AZ80, and ZK60 cast magnesium alloy substrates in an alkaline silicate electrolyte. The corrosion performances of the uncoated and MAO‐coated alloys were investigated using electrochemical and salt spray chamber corrosion tests. The microstructure characterization and experimental results show that among the three alloys studied, the ZK60 Mg alloy exhibited the best and AZ31B the least corrosion resistance under the salt spray conditions. The MAO coating provided robust corrosion protection of the Mg substrates and resulted in a significant decrease in the corrosion rate of the alloys by 3–4 orders of magnitude. The MAO coating on ZK60 alloy showed better corrosion protectiveness than that on the AZ series alloys due to the incorporation of different alloying elements in the coating, especially the Zn and Al elements, which are from the Mg substrate. The corrosion performances and mechanisms of the uncoated and MAO‐coated Mg alloys are interpreted in terms of the microstructure and phase/chemical compositions of both the substrates and coatings.

Effects of an oscillation electromagnetic field on grain refinement and Al8Mn5 phase formation during direct-chill casting of AZ31B magnesium alloy

Abstract The effects of an oscillation electromagnetic field (EMF) generated by low frequency pulse current on the grain refinement and phase formation in direct-chill (DC) casting of AZ31B magnesium alloy have been investigated experimentally. The macrostructure evolution was quantitatively examined in terms of the grain size and its distribution, and fine equiaxed grains can be obtained. Given the Lorentz force and velocity variations, temperature distribution and heat extraction process during DC in different electromagnetic conditions, the grain refinement mechanism and the phase composition and formation of AZ31B magnesium alloy were discussed in detail. The grain sizes decrease from 549 ∼ 1094 μm (without EMF) to 402 ∼ 486 μm at the frequency of 15 Hz, and columnar grain region decreases significantly. Forced convection induced by EMF can strengthen the heat extraction along the diametrical direction of billet, weaken the contact heat transfer between melt and mold wall. For the formation of Mn-containing phases, eutectic transformations are dominant in DC casting process of AZ31B magnesium alloy, and the area fraction of eutectic Al8Mn5 phase decreases from center to edge of billet, and its distribution is more homogeneous in the presence of EMF.

Investigation into the Surface Layer Composition Formed on the Ml19 (Mg–Nd–Y–Zn–Zr) Magnesium Alloy during Melting under Protective Gas Atmospheres

The most currently widespread method of flux-free melting of magnesium alloys is melting under a protective gas atmosphere consisting of inert carrier gas with a small additive of active gas. The ML19 (Mg–Nd–Y–Zn–Zr) casting magnesium alloy contains yttrium and neodymium; these metals are rather active. The interaction of similar alloys with protective gas atmospheres is studied poorly and represents considerable practical interest. Sulfur hexafluoride (SF6) strongly affects global warming; therefore, the application of this gas is limited. In connection with this fact, HFC-R134a is used as active gas in several countries. The influence of protective gas mixtures consisting carrier gas (argon or nitrogen) and active gas (SF6 or HFC-R134a) on the composition of protective layer formed on the surface of the ML19 magnesium alloy melt is considered in this work. A special laboratory setup providing the contact of the protective gas mixture with metal during heating, melting, and solidification of the samples, which excluded the influence of surrounding atmosphere, was developed. The loss of alloying elements turned out to be insignificant, but the Y and Nd content in the alloy when applying nitrogen as carrier gas turned out to be lower than when using argon. The zirconium content was lower in alloys melted using SF6 as active gas. The composition and thickness of oxide films forming when using protective atmospheres SF6 and HFC-R134a are similar. The surface film consists mainly of magnesium fluoride (MgF2) with impurities of oxides, fluorides, and nitrides of zirconium, yttrium, and magnesium. The main distinction of the phase composition of the protective film when applying the HFC‑R134a is the presence of a considerable amount of carbon both in the form of compounds and in the free state. It is also established that a thorough dosage of HFC-R134a in protective atmospheres is required because an increase in its fraction in the gas mixture above 1 vol % leads to severe corrosion of the inner crucible surface during melting, which was not observed when using SF6.

Examination of the surface layer composition formed on ML19 magnesium alloy during melting at protective gas atmospheres

Currently the most common method of the magnesium alloys flux free melting is the melting under the gas protective atmosphere. This atmosphere consists of inert carrier gas with low addition of active gas. The ML19 casting magnesium alloy contains Y and Nd that enough active. The interaction of such alloys with gas protective atmospheres is poorly studied and has serious practical importance. Sulfur hexafluoride (SF6) has a great influence on the global warming and because of that its application is limited. As a result, the number of countries cross over to HFC-R134a as the active gas. This paper presents the investigation of the effect of gas protective mixtures consisting of carrier gas (argon of nitrogen) and active gas (SF6 or HFC-134a) on the composition of protective layer formed on the surface of ML19 magnesium alloy melt. It was developed a special laboratory setup providing the contact of the protective gas mixture with the alloy during heating, melting and solidification of the samples and preventing the influence of the surrounding atmosphere. The loss of the alloying elements was negligible but in the case of using nitrogen as a carrier gas the Y and Nd content in alloy was lower than if the argon is used. If SF6 is used as an active gas, the Zr content in alloys was lower. Composition and thickness of oxide film that formed in both SF6 and HFC-R134a protective atmospheres are mostly the same. The surface film is consist of magnesium fluoride (MgF2) with admixtures of oxides, fluorides and nitrides of zirconium, yttrium and magnesium. The key difference of protective layer phase composition if HFC-R134a used as an active gas is presence of the large amount carbon in the form of compounds and in a free state. Additionally, it was established that using of HFC-134a in protective atmosphere requires more careful dosage given the fact of its percentage in the gas mixture of more than 1 vol.% leads to severe corrosion of the crucible inner surface during the melting.

Cluster compounds formation in metal alloys crystals

The formation and physical origin of the pre-cluster complexes and pre-phase (cluster) compounds have been studied on cast magnesium alloys (in the liquid and solid states) as well as other primary solutions enriched with excess (non-intrinsic, structural) vacancies. The results produced by DSC, TEM observation, Auger-electron, UV-and X-ray photoelectron spectroscopy techniques were combined with positron annihilation, electroresistance, and internal friction measurements to evaluate different stages of the cluster compounds formation and to examine the strength of their chemical bonding in terms of a detailed analysis of electron-sensitive properties. The thermally activated deviations from classical (Arrhenius) behaviour in hydrogen-charged hcp and fcc metal crystals are found to be caused by the nucleation of the solute/excess vacancy complexes. Additional support for this short-range self-supported mechanism comes from data obtained by mechanical spectroscopy and positron annihilation. These pre-cluster separations are assumed to act as nuclei for the synthesis of the cluster compounds such as Mg16Ba2 and Al18Ba9 with own electronic (hybridized) structure in hcp magnesium- and fcc aluminium alloy crystals, respectively. A unified concept of the liquid/solid conversion for condensed cluster-forming alloys is considered. This approach is particularly useful for the development of chemically combined cluster compounds with own electronic configurations as functional materials for high-current electronics.