Papers by Keyword: AZ91

Abstract: Die casting of metallic materials is a highly economical manufacturing process for producing complex functionally integrated components close to the final shape. Thixomolding of magnesium alloys is a special process of die casting. In this process, the magnesium alloy granulate is brought to a semi solid state in a screw conveyor and then injected into the mould. The production of the casting material in the Thixomolding screw allows the temperature conditions to be set for thermally controlled solid content. These are produced by heating the Mg granulate above solidus temperature and have significantly lower casting temperature compared to conventional die casting.In this study, a flow length tool for semi solid AZ91 is designed and flow length tests are performed. Also the general use of a composite material cores in semi-solid magnesium Thixomolding and their influence on flow length are investigated. Cast-in cores allow the reproduction of complex internal hollow geometries of castings or the integration of special materials.

Abstract: The present paper deals with the study of magnesium alloy hybrid composites. AZ91 is a popular magnesium alloy with good specific strength at room temperatures. However, it suffers with poor mechanical properties at elevated temperatures. The reinforcement materials can be prepared by polymers and ceramic particles. The selection of proper material will have a greater response on the properties. Therefore, in order to increase the mechanical responses, preparation of composites is good idea with low cost. To ensure multiple properties, it is always necessary to go with Hybrid composites. In this context, this paper reviews the materials used in the fabrication of composites, fabrication Techniques, microscopic behaviours and mechanical responses. This paper also provides research potentials along with the latest developments in the area of AZ91 Composites.

Abstract: The investment casting into a ceramic shell of magnesium alloys brings several difficulties, one of which is the high reactivity of some magnesium alloys with the often-used ceramic shells. In the group of these potentially problematic alloys belong the AZ91 magnesium alloy too. This paper aims to describe the interaction of magnesium melt with ceramic shell, especially from the point of view of manufacturing problems on the surface of emerging defects with reduced corrosion resistance. Samples of AZ91 magnesium alloy castings in as-cast and heat-treated were microstructurally evaluated. Surface defects were analysed using light and scanning electron microscopy, including their EDX chemical microanalysis.

Abstract: In modern engineering low-density composites plays a vital role of which magnesium alloys are very effective due to its high strength with better corrosion resistance and neat cast ability. In this work a micron sized Boron carbide ceramic (B₄C) of about 100 microns is diffused as a reinforcement with AZ91 for preparing a magnesium metal matrix composite (MMMC) through stir casting route. A modified pit furnace setup is used for doing stir casting with varying volume fractions of 0％ and 3% of boron carbide for doing the composites. Furthermore mechanical and metallurgical properties like Tensile test is made through universal testing machine, Micro-hardness through Vickers hardness tester and Micro structure through Optical Microscopy is done for investigation.

Abstract: In this paper tensile properties at elevated temperature of extruded AZ91 magnesium alloy and the same alloy further processed by ECAP (exECAP) are compared. The tensile tests were performed at room temperature and for the temperature range of 100 to 300 °C. Loading speed 2 mm/min was used for the tests. At room temperature mechanical properties except elongation were slightly higher for extruded material yet still very similar to properties of exECAPed material. Overall trend of properties evolution with increasing temperature was also similar but the decrease of strength or the increase of elongation and reduction of area respectively is more intensive for exECAPed material. Elongation of exECAPed material exceeded elongation of extruded material more than twice at 300 °C and with value of ~260% this alloy exhibited pseudosuperplastic behavior.

Abstract: Powder metallurgy metal matrix composites based on AZ91 alloy matrix reinforced with 0.3, 0.6 and 0.9 weight percent of multiwall carbon nanotube (MWCNT) were investigated from the point of view of their response to artificial ageing as compared to the unreinforced AZ91 matrix alloy. Mg-Zn-Al (AZ91) and its composite were prepared by milling the raw materials and followed by sintering at 450°C for 2 hours. The sintered samples were solution treated at 415°C for 2 hours and followed by artificial ageing at 175°C. The ageing behavior was monitored by following the phase analysis and hardness of the samples examined. Microstructure of the sintered composites indicated that MWCNT was embedded in the AZ91 matrix alloy. All composites indicated lower hardness than matrix, however AZ91reinforced with 0.6 and 0.9 weight percent of CNT showed accelerated ageing. X-ray diffraction pattern indicated the present of β-phase (Mg₁₇Al₁₂) that responsible for the hardening behavior.

Abstract: In the present work the effect of heat treatment on the hardness behavior of AZ91 and AZ91 reinforced carbon nanotube were investigated under FESEM, Xrd and Rockwell hardness tester. Cnt was embedded homogenously into the matrix due to successfully mechanical alloying using planetary milling. Kinetic precipitation of β-phase (Mg₁₇Al₁₂) also reveal in the X-ray diffraction pattern. Meanwhile, the artificial aged nanocomposite found decreased in hardness, compare to monolithic has higher value form early aged until 36 hours aging.

Abstract: In this study, aluminum sheet metal reinforced magnesium structures have been manufactured by high pressure die casting (HPDC). Selected interfaces of the hybrid structures were analyzed before and after exposure to corrosive environments. The characterization of the as cast bounding surfaces of aluminum sheets and magnesium cast alloys was carried out to quantify the appearance of crevices, which are significantly influencing the extent of the corrosive attack. Depending on the geometrical design of local bonding areas, the observed interface conditions varied from defect-free form closure to crevice widths beyond 35 μm. A minor percentage of the analyzed segments revealed areas of local metallic continuity, detected as intermetallic phases Al₃Mg₂ and Al₁₂Mg₁₇. In order to evaluate acting corrosion mechanisms, hybrid samples featuring the material combinations EN AW 5083 + AZ91 HP and EN AW 6082 + AM50 HP were subjected to immersion tests using 0.1M NaCl solution at a pH of 7.5. The results showed a strong influence by the spread of the potential difference. Alternating corrosion tests (VDA 621-415) were applied to prove effectiveness of cathodic dip coatings (CDP) and wax sealing on standard profile structures, since the uncoated Al-Mg samples sustained severe corrosion damages immediately.

Abstract: In recent years an interest in magnesium and magnesium alloys not only for the automotive industry but also for medical applications was increasing due to the low density and good specific strength. Magnesium alloys show good castability but lower ductility and strength than wrought materials. For this reason, refinement of grains and homogenous distribution of intermetallic phases are needed to improve formability and mechanical properties. On the other hand, the degradation of the material by corrosion is influenced by the grain size and phase distribution. This work investigates the microstructure evolution of pure Mg and magnesium alloy AZ91 by friction stir processing (FSP) technique. FSP experiments are carried out by constant force, optimizing the rotation and feed rate to obtain a homogenous microstructure, free of defects stir zone, good surface finishing and stable conditions during the process. The results show that the grain size is affected by the spindle speed. Increasing the number of passes reduces also the size of the grains and the intermetallic phases in the AZ91 alloy. The overlapping of passes between overlapping ratio 0.5 to 1 determines an uniform depth of the stir zone over a larger surface area.Hardness measurements are performed to evaluate the influence of FSP parameters on the mechanical properties. The degradation rate of the studied FSP Mg alloys is determined by hydrogen evolution in corrosion immersion tests, which depend strongly on the phase distribution and grain size.

Abstract: Magnesium alloys create increasing interest in structural application where weight reduction is vast concern. However, one of magnesium drawback in various applications is low corrosion resistance. In general, a hard coating can be applied on metal to combat such a problem. AlN and TiN coatings are most widely utilized in manufacturing area i.e for structural application due to its high hardness, high chemical stability, and excellent adhesion to substrates. Most recent, TiAlBN coating catch many attentions due to its superior properties than other most studied hard coating. The incorporation of aluminium in the cubic face centered TiN structure on Ti sites leads to deformation and strengthening of the crystal structure of the coating together. Moreover, incorporation of BN in this coating should improve and enhanced the corrosion resistance of Mg alloy. Therefore, in this study, TiAlBN coating have been chosen to be deposited on Mg alloy using reactive magnetron sputtering together with AlN and TiN coatings for comparison study. During depositions, target power, working pressure and bias voltage are optimized for each coating. Analysis on the effect of AlN, TiN and TiAlBN coatings on Mg alloy substrate include thickness measurement and microstructure by scanning electron microscope (SEM). Coatings phase were analysed using glancing angle X-ray diffraction analysis (GAXRD) and corrosion properties were evaluated using potentiodynamic polarization in NaCl solution. TiAlBN shows better performance of corrosion protection with the least corrosion rate (penetration rate = 0.20 mm/yr; mass loss rate=0.97g/m²d) in sodium chloride (NaCl) solution although having the lowest coating thickness (412 nm).