Papers by Keyword: Die Cast

Abstract: Aluminum with –2.5wt.% Cu–2.5wt.% Mg – 5wt.% Zn alloy was synthesized by die cast and spray formed technique. The average density of die cast and spray formed Al alloy was measured by water displacement method. The compression strength, hardness and tribological properties of the Al alloy produced by die cast and spray formed technique was studied as per the ASTM test standards and recorded the average values. The surface morphology of die cast Al alloy depicts the dendritic structures and spray formed Al alloy contains the equiaxed grains, coarse grains and fine grains across the surface. The elemental analysis of both die cast and spray formed Al alloy was measured by using scanning electron microscope. Average percentage of porosity of die cast and spray formed aluminum alloy is 1.79 ± 0.23 and 1.10 ± 0.3 respectively. The hardness of spray formed Al alloy is 10.54 % lesser than that of die cast Al alloy. Average ultimate compression strength of spray formed and die cast Al alloys are 360.07 ± 9.58 MPa and 353.33 ± 5.56 MPa respectively. The study also recorded the wear rate and coefficient of friction of die cast and spray formed Al alloy at different load and speed conditions. The precipitation strengthening mechanism is found to be involved in spray formed alloy.

Abstract: Motorbike shock absorbers of gravity die cast aluminum A356.0 alloy were being imported in the as-cast condition and later on machined at local foundries and workshops by sub-vendors to achieve the required dimensions and on many occasions a nearly complete solid block was cast and machined to achieve the desired shape but this process not only lowered the metallic yield but also the high machining costs and time required made it very uneconomical. Motorbike shock absorbers are critical vehicle components which are always under load and must never fail suddenly without warning therefore they need to be free of defects like shrinkage and micro-porosity. The thin wall thickness of 6mm and troublesome nature of cores required makes this component quite difficult for the conventional metal caster. The current research paper deals with the methoding, die designing, modeling and simulation, optimization and finally casting of these components following the data produced by the former. Initially a single piece per mold was suggested but later on considering the economics of the project two pieces i.e. left and right were recommended to be cast from a single sprue in each die with a vertically parted permanent die mold. For the methoding calculations the Thermal modulus has been used instead of the conventional casting modulus and for gating the naturally pressurized system is incorporated. Throughout the simulation process a significant number of iterations were made to achieve the final design which ensured a laminar flow of liquid aluminum below the critical velocity limit; the actual die casting results yielded good comparison with the simulation studies showing shrinkage cavity away from the risers and micro-porosity only in ingates.

Abstract: In order to study the environmental effect on fatigue properties of die-cast magnesium alloys, several fatigue tests were performed for AM50HP and AZ91HP in ambient air, vacuum, engine oil, deionized water and 3.5% NaCl solution. It is found that the S-N curves are steeper in corrosive environment and AM50HP shows a higher sensitivity to the action of 3.5% NaCl solution than AZ91HP. Both alloys do not have endurance limits in 3.5% NaCl solution, whereas endurance limits could be detected in ambient air, which are about 90MPa and 100MPa for AZ91HP and AM50HP respectively. It is also found that FCP rate is substantially increased in corrosion media: the presence of oxygen causes the production of oxide film on the fresh surfaces made during the cyclic loading and the oxide film would restrict the deformation of the matrix beneath the hard film and promote hydrogen embrittlement in the wet condition.

Abstract: This paper shows a study of correlation between EDM´s parameters with the level of superficial defects development, which can lead to premature failure of die cast mold machined by EDM. The correlation of parameters was determined through experimental matrix that uses the DOE methodology (Design of Experiment). In order to evaluate the surfaces of some machined samples a stereo optical microscopy, SEM (the scanning electron microscope) and a micro hardness profile machine were used. The results show that in the worst machining condition, which is caused by association of long electric discharge pulse time-on and graphite machine-electrode, it is possible to minimize the amount of surface defects, without applying a subsequent machining process such as polishing, just using the reduced time-on´s electric discharge pulse, copper electrode and dielectric fluid with base of hydrocarbon.

Abstract: New die cast magnesium alloys have increasingly been developed in recent years for the automotive industry due to their high potential as structural materials for low density and high strength/weight ratio demands. However, their poor mechanical properties and low corrosion resistance have led to a search for new kinds of magnesium alloys with better strength, ductility, high temperature behaviour and high corrosion resistance. The main objective of this research is to investigate the corrosion behaviour of new die cast magnesium alloys: Mg-Al-Ca, Mg-Al-Sr. AC and DC polarization tests were carried out on the new alloys. Microstructure was examined using optical and electron microscopy (SEM) and EDS. The additions of Sr and Ca affected the corrosion behaviour. These results can be explained by the effects of alloying elements on the microstructure of Mg alloys such as grain size and precipitates caused by the change in precipitation.

Abstract: Creep rupture tests were performed for a die-cast Mg-Al-Ca alloy AX52 (X representing calcium) at 29 kinds of creep conditions in the temperature range between 423 and 498 K. The creep curve for the alloy is characterized by a minimum in the creep rate followed by an accelerating stage. The minimum creep rate (ε& m) and the creep rupture life (trup) follow the phenomenological Monkman-Grant relationship; trup = C0 /ε& m m. It is found for the AX52 die-cast alloy that the exponent m is unity and the constant C0 is 2.0 x 10-2, independent of creep testing temperature. The values of m and C0 are compared with those for another die-cast magnesium alloys. The value m=1 is generally detected for die-cast magnesium alloys. On the contrary, the value of C0 sensitively depends on alloy composition, which is reduced with increasing the concentration of alloying elements such as Al, Zn and Ca.

Abstract: In the present paper, phosphoric and chromic conversion coatings were prepared for the die-cast magnesium alloy ZM5. Both two kinds of chemical converting coatings are of evident corrosion resistance. Their compositions, morphologies and crystal characteristics were discussed.