نشریه ریخته گری
پیاپی 95 (بهار و تابستان 1389)

Distinct effects of liquid filtration and modification of A356 aluminum alloy and also their joint effects on mechanical, fatigue life and tribological properties of the alloy have been investigated. Properties of cast specimens from different baths of unprocessed liquid, filtered liquid, Sr-modified liquid and filtered-modified A356 alloy liquid have been evaluated. The results demonstrates that the filtration or the modification of liquid has its own individual effect on the properties and either one improves mechanical, fatigue and tribological properties of the alloy. The joint effect of liquid filtration and modification on properties of the alloy is fairly equal to the sum of the individual effect of each one. Filtration and modification of the A356 liquid improve UTS, elongation and lowcycle fatigue life of the alloy by 38, 46.5 and 175% respectively. It also reduces friction coefficient and wear loss weight by 30 and 40%.

In current research, the effect of Sr and Ca modification on the microstructure and tensileproperties of Al-15%Mg2Si composite have been investigated. The coarse reinforcement of the primary Mg2Si particles in the normal composite leads to poor properties. Therefore, the composite with coarse primary Mg2Si particles need to be modified to obtain adequate mechanical strength and ductility. It has been reported that rare earth, potassium fluotitanate, sodium salt or melt superheating treatment have the power to modify the morphology of primary Mg2Si.The microstructural results showed that, with the increase of Ca content, primary Mg2Si morphology changes and average size of Mg2Si particles decreases. Also, with Sr addition, the primary Mg2Si morphology changes from polygonal to quadrangle shape. The results showed that the optimum amount of Sr and Ca are 0.2% and 0.5% respectively. Adding Sr and Ca also showed significant effect on UTS and El%.

In this work, a high chromium containing cast iron with composition 2.4C-15Cr-1Mo was produced through conventional and semi-solid casting. Specimens were destabilised at 1000oC for 2, 3 and 4 hours and cooled in air. Samples were reheated up to 300, 350,400,450,500 and 550 oC for 2 hours again. All heat treated and cast specimens were etched in 2% nital solution and their microstructure was studied by optical and Scanning Electron Microscopy (SEM). Afterward, hardness and micro hardness and XRD analysis were carried out. Microstructures reveal that alternations in eutectic phase morphology and distribution of alloy elements in primary austenite and eutectic carbide in semi-solid cast iron, result in a homogenous dispersion of secondary carbides in grains. Maximum hardness in semi-solid and conventional cast irons after heat treating at 1000oC for 2 hours was 61.3HRC and 61.6HRC respectively and after 3 hours was 61.5HRC and61.7HRC.

In this research, the effect of argon gas blowing time and melt temperature during degassing in A356 aluminum alloy investment casting for fabrication of Hinge parts were investigated. After mold and wax model preparation, melt degassing was performed by argon gas for 2-10 minutes and 20 liter/hour volume flow rate and also melt temperature 700-750°C in 15 different conditions, eventually hinges were cast by investment casting. Dimensional inspection, X-ray radiography, tensile and hardness tests were performed for determination of best state among various conditions. Results showed that the time of argon flow had no effect on hardness whereas increase of blowing time improved tensile strength because of better degassing. Also at experimental temperatures, the temperature of melt had no effect on quality of castings.

In this research, effect of Al-10Sr-1Ti-2B master alloy has been studied on the microstructure and solidification characteristics of 380.3 aluminum alloy. Thermal Analysis has been used as a technique to study the cooling curves and first derivative curves. Effect of integrated grain refiner and modifier on solidification parameters such as α-Al dendrite growth temperature (G. T α), α-Al dendrite recalescence undercooling (G. T α Δ), eutectic silicon growth temperature (G. Si T) and eutectic silicon recalescenceundercooling (G. Si ΔT) has been determined. By increasing master alloy content, G. T α and G. Si ΔT have been increased, but, G. T α Δ has been decreased, and G. Si T increases firstly and then decreases. (, Al Si E G ΔT −) can be used as a parameter to control the modification of eutectic silicon. The results of this research indicate that the optimum level of Al-10Sr-1Ti-2B master alloy for the grain refinement and modification of 380.3 alloy is about 0.5 wt%.

In this research effect of wetting agent and antifoam on slurry behavior such as PH, density and flow time and surface quality, thickness of first layer and strength of ceramic shell moulds was investigated. Five slurries with the same amount of binder and refractory with different amount of wetting agent and antifoam were prepared. MOR and thickness of first layer were measured and surface quality of ceramic shell was observed using micro-stereo microscope. According to the experimental results flow time decreased with increasing wetting agent but ceramic shell first layer and strength increased. At the same time with increasing amount of antifoam flow time decreased and first layer and strength of ceramic shell moulds decreased. The best surface quality was produced with the balanced amount of wetting agent and antifoam.

The aim of this article is to study the effect of thermal treatment and adding chromium, during the casting, on mechanical and wear behavior of modified Cr-Mo casting steel alloy. Comparison of numerical simulation, which was done by Procast software, with practical results showed that the places which fractures happened, are dependent on hot and chill zones in the casting parts. Therefore, the casting needs to heat treat to eliminate thermal residual stresses and metallurgical stresses. Results of the optical and electron microscopy, hardness, impact and tensile tests in order to studying the wear properties of main and modified specimens showed that adding chromium and heat treatment cycle with controlled cooling rate to obtain superfine pearlitic structure, present the best wear resistance by increasing strength. This structure could improve the lifetime of the castingup to 5000 hours.