Magnesium alloy tubes have good formability at elevated temperatures. In this study, a finite element code DEFORM 3D is used to simulate the result of T-shape hydroforming at working temperatures 150¢J and 250¢J with magnesium alloy AZ61 tubes and then conducts the hydroforming experiments. By modifying the loading paths, products with uniform thickness and branch height are obtained 49mm. The results of simulation are compared with the experimental results to verify the validity of this modeling. On the other hand, the effects of the die fillet radius on tube formability during y-shape hydroforming are discussed. With the right die fillet radius r1¡×10mm and the left die fillet radius r2¡×30mm, a better formability of the tube is obtained.

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A recent study on the Post-Formed properties of Superplastically Formed Magnesium AZ31B has shown that the heating time prior to testing has a major effect on the Post Forming properties of the superplastically material. To this point, there has been very little examination into the effect of pre-heating or annealing on superplastic forming (SPF) properties. In this work, the effects of annealing prior to the SPF of Mg AZ31 alloy were examined. Both high temperature SPF tensile and bulge specimens were formed after annealing. Multiple annealing temperatures were examined to produce specimens with grain sizes ranging from 8 andamp;igrave;m to 15 andamp;igrave;m for comparison with traditional SPF results. The results show that the effect of annealing can be suitable for the improvement of thinning and possibly the forming time of superplastically formed Magnesium alloys through the control of the microstructure.

Pure magnesium (Mg) and its alloys with calcium (Ca) and both Ca and zinc (Zn) have potential as bioresorbable bone implant materials provided the corrosion rate can be controlled. Thus, corrosion behaviour was investigated for pure Mg, Mg-2Ca, and Mg-2Ca-1Zn cast alloys subjected to either no heat treatment or to solutionizing and aging heat treatment. In addition, corrosion behaviour was investigated for surface modifications involving the deposition of silver (Ag) nanoparticles. These materials and constructs were all nominally biocompatible in that they would not elicit a strong and immediate adverse tissue reaction when implanted in bone. Static immersion tests in Hanks’ balanced salt solution were performed to evaluate the corrosion behaviour. The Mg-2Ca alloy exhibited the highest corrosion rate when compared with pure Mg and Mg-2Ca-1Zn for any length of immersion time. For short immersion times (48 hours), solutionizing followed by natural aging reduced the corrosion rate of Mg-2Ca alloy, but this heat treatment did not seem to have an effect on the corrosion rate of Mg-2Ca-1Zn alloy. As well, for short immersion times (48 hours), solutionizing and artificial aging also did not seem to have a large effect on corrosion rates for either Mg-2Ca or Mg-2Ca-1Zn, when compared to solutionizing and natural aging. Corrosion behaviour of surface-modified samples was sensitive to certain features of the Ag depositions. It was found that when the deposited Ag tracks were thick and wide, the corrosion rate of Ag-deposited samples increased significantly when compared to samples without any Ag deposition. However, when the Ag tracks were thinner and somewhat narrower, the corrosion rate did not appear to be much higher than that of samples without Ag deposition. Therefore, controlled Ag deposition may not be too detrimental to the corrosion behaviour of Mg and Mg alloys. The corrosion product morphology appeared to be similar for both the samples deposited with Ag and samples without any Ag. Needle-like formations were observed in small areas on the corroded surfaces. X-ray diffraction revealed Mg(OH)₂ as the main corrosion product. Because energy dispersive X-ray analysis consistently revealed multiple elements in the corrosion products (such as Mg, O, Ca, P, small amounts of C, and sometimes Cl), it was concluded that other compounds (possibly hydroxyapatite, magnesium chloride, and/or magnesium- and calcium-containing phosphates) may have formed in addition to the Mg(OH)₂.

In the present investigation, surface coatings employing laser surface alloying (LSA) and plasma electrolytic oxidation (PEO) processes have been prepared on Mg alloys. The coatings have been investigated for corrosion and wear behaviour. Two important Mg alloys based on Mg–Al system were selected namely, MRI 230D and AM50 as substrates. LSA coatings have been prepared employing Al and Al2O3 as precursors using different laser scan speeds. PEO coatings were prepared in standard silicate and phosphate based electrolytes employing unipolar, pulsed DC. Hybrid coatings using a combination of the two processes were also produced and investigated for corrosion and wear behaviour. Hybrid coatings of LSA followed by PEO (LSA+PEO) were investigated for effectiveness of sealing the cracks in the LSA coatings by subsequent PEO process and consequent improvement in the corrosion resistance. Hybrid coatings of PEO followed by LSA (PEO+LSA) were prepared with an objective of sealing the pores in the PEO coating LSA treatment. In an attempt to produce more compact PEO coatings, electrolyte containing montmorillonite clay additives was employed for the PEO process of AM50 Mg alloy. The coatings were produced employing different current densities and the effect of current density on the microstructure and corrosion behaviour of coating was investigated. Electrochemical corrosion tests of uncoated and coated alloys were carried out in 3.5 wt.% (0.6M)NaCl, neutral pH, solution with an exposed area of 0.5 cm2 for a time duration of 18.5 h. For the PEO coatings with clay additives, corrosion tests were conducted additionally in 0.5 wt.% (0.08 M) NaCl, neutral pH, solution for a time duration of 226.1 h. Wear behaviour of LSA coatings was analyzed by employing a pin on disc tribo–tester conforming to ASTM G–99 standard at ambient conditions with ground EN32 steel disc of hardness Rc 58 as the counterface. Tests were conducted under dry sliding conditions for a sliding distance of 1.0 km at a sliding velocity of 0.837 m/s employing normal loads of 10, 20, 30 and 40 N. Friction and wear behavior of PEO and PEO+LSA coatings were analyzed at ambient conditions by employing a ball−on−flat linearly oscillating tribometer conforming to ASTM G–133 standard. AISI 52100 steel ball of diameter 6 mm was employed as the friction partner. Wear tests were conducted under dry sliding conditions for a total sliding distance of 100 m at normal loads of 2 N and 5 N with oscillating amplitude of 10 mm and mean sliding speed of 5 mm/s. LSA coatings could not improve the corrosion resistance of MRI 230D Mg alloy. This was attributed to the presence of cracks in the LSA coating, which resulted in the accelerated galvanic corrosion of the substrate. LSA coatings improved the wear resistance at all loads. The improved wear resistance was attributed to β (Mg17Al12) phase and Al2O3 particles in the coating which increased the hardness of the LSA layer. No trend in corrosion and wear resistance with laser scan speed was observed for LSA coatings. PEO coatings improved the corrosion resistance of the MRI 230D Mg alloy significantly. The improved corrosion resistance was attributed to the enhanced barrier protection provided by dense barrier layer formed at the substrate/coating interface and to the insoluble phase constituents in the coatings. PEO coating was effective in improving the wear resistance at low loads/contact pressures. At higher loads, the coating underwent micro–fracture as a result of the porosity in the coatings. Hybrid coatings of LSA followed by PEO (LSA+PEO) in silicate based electrolyte improved the corrosion resistance of LSA coatings. However, the corrosion resistance was not improved to the extent of PEO coatings on as–cast alloy as a result of cracks in the primary coatings, which were not fully sealed by the plasma conversion products. No trend in corrosion resistance with laser scan speed was observed for LSA+PEOcoatings. In hybrid coatings of PEO followed by LSA (PEO+LSA), primary PEO coating was completely melted and mixed with applied precursor to form a single composite LSA layer. The corrosion resistance of the hybrid coatings was observed to be lower than that of the as–cast alloy. The presence of solidification cracks reduced the barrier properties and resulted in the accelerated galvanic corrosion of the substrate similar to LSA coatings. Hybrid (PEO+LSA) coatings exhibited improved wear resistance as compared to as–cast alloy at lower loads as a result of increase in the hardness due to β (Mg17Al12) phase and oxide/ceramic particles in the hybrid layer. At higher loads, hybrid coatings exhibited higher wear rate as compared to as–cast alloy and PEO coatings. This was attributed to three–body abrasive wear as a result of dislodged hard oxide/ceramic particles in the wear tracks. No trend in corrosion and wear resistance with laser scan speed was observed for PEO+LSA coatings. PEO coatings on AM50 Mg alloy by employing clay additives in the electrolyte resulted in the reactive uptake of clay particles producing a predominantly amorphous coating at low current density. Clay additives were effective in improving the compactness of the coating at lower current density. At higher current densities, the porosity of the coatings increased. The clay particles got re–constituted producing increasing amount of crystalline phases with increase in current density. Long term impedance measurements showed that clay addition as well as increased current density employed for the PEO process was not effective in improving the corrosion resistance of the coatings. At low current density, even though the coating with clay additives was more compact, it was deficient in MgO and consisted predominantly of an amorphous phase, which underwent fast dissolution in electrolyte thereby resulting in an early loss of barrier properties. At higher current densities, even though the coatings consisted of increased amount of MgO and crystalline phases, which resist dissolution in the electrolyte, the increased porosity and defective barrier layer resulted in easy permeation of the electrolyte into the substrate/coating interface, which resulted in much earlier loss of barrier properties and inferior corrosion resistance.

As ligas de magnésio atraíram a atenção novamente nos últimos anos por causa de suas propriedades de baixa densidade, resistência à tração e rigidez específica. Por outro lado, a maior limitação para o uso de ligas trabalhadas é a baixa conformabilidade em temperatura ambiente devido à estrutura hexagonal compacta (HCP) das ligas. O presente trabalho de pesquisa teve como objetivo estudar o encruamento, recristalização e crescimento de grãos durante a laminação de liga magnésio AZ31B em alta e baixa temperatura, analisando a evolução da microestrutura, da textura e a variação das propriedades sensíveis à microestrutura. A liga AZ31B é sensível à taxa de deformação em alta temperatura, entretanto, a anisotropia é negativamente afetada na laminação a frio, portanto, apresenta uma melhor laminação na faixa de temperaturas de 200 a 300ºC, devido ao refinamento de grãos, causado pela recuperação e recristalização dinâmica. O estudo foi realizado em amostras de uma chapa de liga de magnésio AZ31B recristalizada (2 mm de espessura). Amostras foram deformadas por laminação em temperaturas diferentes (25, 100, 200, 250 e 300ºC) e com diferentes taxas de deformação. A caracterização microestrutural foi realizada com auxílio de várias técnicas complementares de análise microestrutural, tais como microscopia óptica, microscopia eletrônica de varredura, análise de raios-X por dispersão de energia, difração de raios X e microdureza Vickers. A deformabilidade e a ocorrência de recristalização dinâmica e crescimento de grãos mostraram forte dependência com as condições de laminação. Na laminação a frio, o refinamento de grão foi mais efetivo com baixas taxas de deformação (1,6 s-1) do que na laminação a quente. Entretanto, a intensa textura basal foi enfraquecida em temperaturas próximas a 300ºC e com taxas de deformação próximas a 3,5 s-1. A ductilidade das ligas pode ser melhorada em altas temperaturas de deformação, pelo refinamento dos grãos que produz a diminuição da fração volumétrica das regiões macladas e pelo aumento do número de sistemas de deslizamento, além do enfraquecimento da intensa textura basal, característica das ligas de magnésio. / Magnesium alloys have attracted the attention again in recent years because of their low density, their specific tensile strength and rigidity. However, the greatest limitation for the usage of wrought magnesium alloys is their poor formability at room temperature due to the hexagonal closed packed (HCP) crystal structure. The present research focused on study the work-hardening, recrystallization and grain growth during rolling of AZ31B magnesium alloy at low and high rolling temperature. It was made through the analysis of microstructure and texture evolution and variations of microstructure-sensitive properties. The AZ31 magnesium alloy is sensitive to strain rate at high temperature, meanwhile, the anisotropy is adversely impacted in cold rolling sheets. Thus, AZ31B magnesium alloy exhibits better workability in 200-300°C temperature range due to the grain refinement caused by dynamic recovery and dynamic recrystallization. This research was carried out on samples of recrystallized sheet (2 mm in thickness). Samples were deformed by rolling at different temperatures (25, 100, 200, 250 and 300°C), using different strain rates. Microstructural characterization was done by using several complementary techniques of microstructural analysis, such as optical microscopy, scanning electron microscopy, X-ray analysis by energy dispersive, X-ray diffraction and Vickers microhardness tests. A competition between dynamic recrystallization and grain growth depends on rolling conditions. Low strain rate (1,6 s-1) at cold rolling improved more effective in refining grains than warm rolling. Meanwhile, the intense basal texture was weakened at 300°C with a high strain rate of 3,5 s-1. The ductility of magnesium alloys can be greatly improved at high temperature, with a fine grain structure that causes the reduced volume fraction of twins, and an increase the number of slip systems, weakening the intense basal texture, rather characteristic for magnesium alloys.

Because of its low density and high strength, magnesium (Mg) and its alloys are being sought after in the automotive industry for structural applications. Although many road-going cars today contain cast Mg parts, in the fabrication of chassis structural members the wrought alloys are required. One of the challenges of fabrication with wrought Mg is welding and joining the formed sheets. Because of the commonly observed difficulties in fusion welding of Mg such as hot cracking and severe Heat Affected Zone (HAZ), this work aimed to establish the feasibility of the solid-state process Magnetic Pulse Welding in producing lap welds of Mg sheet. Mg AZ31 alloy sheets have been lap-welded with Magnetic Pulse Welding (MPW), an Impact Welding technique, using H-shaped symmetric coils connected to a Pulsar MPW-25 capacitor bank. MPW uses the interaction between two opposing magnetic fields to create a high speed oblique collision between the metal surfaces. The oblique impact sweeps away the contaminated surface layers and forces intimate contact between clean materials to produce a solid-state weld. Various combinations of similar and dissimilar metals can be welded using MPW. Other advantages of MPW are high speed, high strength, and the possibility of being mounted on a robotic arm. The present research focuses on the feasibility and mechanical performance of an MPW weld of 0.6 mm AZ31 Mg alloy sheets made in a lap joint configuration. Tensile shear tests were carried out on the joints produced. Load bearing capacity showed linear increase with capacitor bank discharge energy up to a certain value above which a parabolic increase was seen. Strength was estimated to be at least as high as base metal strength by measuring the fracture surface area of selected samples. The fracture surface of samples welded at higher discharge energy showed two regions. In the beginning of the bond a platelet-featured fracture brittle in appearance and a ductile, micro-voiding fracture in the latter part. The joint cross section morphology consisted of a flattened area that had two symmetric bond zones 1 mm wide each separated by an unbonded centre zone ~3mm wide. Reasons for the morphology were presented as a sequence of events based on the transient nature of the oblique collision angle. The interface microstructure was studied by optical and electron microscopy. Examination of the bonds has revealed sound and defect free interfaces. No microcracking, porosity, resolidification, or secondary phase formation was observed. Metallographic examination of the unbonded centre zone revealed anisotropic deformation and a lack of cleaning from the interface. This zone is formed as a result of normal impact in the initial stage of collision. The bond zone interface of the joint was characterized by a smooth interface consisting of refined grains. In samples welded at higher energy interfacial waves developed in the latter half of the bond zone. Transmission electron microscopy (TEM) of the bond zone revealed a continuous interface having an 8-25 μm thick interlayer that coincided with the waves and had a dislocation cell structure and distinct boundaries with adjacent material. Equiaxed 300 nm dynamic recrystallized (DRX) grains were found adjacent to the interlayer as well as other slightly larger elongated grains. The interlayer is thought to be formed in plasticized state at elevated temperature through severe shear strain heating. The interlayer corresponds to a ductile fracture surface and, along with the interfacial waves, is responsible for the joint’s high strength.

This study is to analyze and test the extrusion process of a hollow spur gear and a solid helical product with magnesium alloy. In the hollow spur gear part, firstly, a design criterion to determine the forming parameters is proposed. Then, the Finite Element Analysis is used to simulate the flow pattern of the billet from separating channel, welding chamber to die bearing part. From a series of simulation results, the effect of separating channel length, mandrel entrance angle, welding chamber height, etc. on the radial filling ratio, welding pressure, extrusion load, etc. are found. By using the Taguchi Methods, we can find the most important parameters. Finally, a better die geometry is designed to obtain a sound product. In the helical product part, the Finite Element Analysis is used to get the understandings of radical filling ratio of magnesium alloy in the helical zone. Then, a better die geometry is designed from the results of analyses. Finally, hot extrusion experiments of a hollow spur gear and a solid helical product are conducted. The experimental values of the extrusion load and the product¡¦s dimension are compared with the analytic values to verify the validity of the analytic models.

Screws are produced by four manufacturing processes : extrusion, drawing, heading and thread-rolling. This paper will develop the related manufacturing technology of LZ91 magnesium alloy screws. At first, finite element simulation is adopted to analyze the effects of each process parameters on the formability. Then, each process experiments are conduted to manufacture an M6 magnesium alloy screw. Comparisous between analytical and experimental results verify the suitability and accuracy of the analytical models. In the extrusion process, by the finite element simulations the extrusion load is obtained. Then bar extrudsion experiments with high extrusion ratioto manufacture two bars of 6.5 and 7 mm in diameter using a 350 ton extrusion machine . In the drawing process, the effects of reduction and friction factor on the optimal semi-die angle are discussed, and the relationship is found. Then a rod of 7.0 mm in diameter is drawn into 6.5 mm experimentally. In the heading process, three stages in it`s process are designed. The arc shape and axial length of the die for the first stage are found out. Finally, heading experiments are conducted and sizes between the product and the simulation results are compared. In thread-rolling process, the effects of the screw plate gap on the formability are discussed numerically. Then, thread-rolling experiments are conducted to compare the sizes of the product and the simulation results. In addition, microstructure observation and hardness test are conducted to understand the effects of drawing process on the strength of the product.

The thesis aims to investigate the mechanical behavior and properties of a centrally notched hybrid Magnesium/Carbon-Fiber/PEEK laminate at elevated temperature. The high performance hybrid composite laminates of 0.5mm Magnesium sheets sandwiched by Carbon-Fiber/PEEK (APC-2) guasi-isotropic and cross-ply laminates were fabricated. The Magnesium sheets were polished and cleaned by acetone, then underwent the surface treatment by CrO3-base solvent etchants, cured by the improved diaphragm curing process. The finished laminates were cut into the specimen than drilled a 4mm diameter hole in the center of specimen. At first, the ultimate strength, stiffness and stress-strain diagram were obtained due to static tension tests at elevated temperature, such as 25¢XC(RT), 75¢XC, 100¢XC, 125¢XC, and 150¢XC. Compare of them, the notched quasi-isotropic ones drop almost 50% in strength, and the notched cross-ply ones are half of unnotched ones. The two lay-up notched specimens are slightly below the unnotched ones in stiffness. The strength of the specimens are decrease as temperature rise. As the temperature rise the stiffness of quasi-isotropic ones drop, but it just change little in cross-ply ones. Then the notched specimen fatigue life and load-cycle (P-N) curves were obtained by tension-tension fatigue test. The P-N curves were adopt to prevent the stress concretion of the notched specimen. Consider the same loading, notched specimens has worse fatigue behavior, but in the same load ratio, the normalized P-N curves of the unnotched ones were below the notched ones means notched ones has better fatigue behavior. Recording the specimen image by video camera during the testing process, the cracks at the edge of hole were found. However delamination was not found. Necking was observed in quasi-isotropic specimens, but not in cross-ply. Observed by optical microscopy, the improved surface treatment will decrease the probability of delamination from 20% to less than 10% after hot press.