نشریه ریخته گری
پیاپی 104 (بهار 1393)

In this paper, the two-step casting (TSC) method has been used to produce the functionally Si-gradient Al-Si alloys. For this purpose, the hypereutectic LM28 (393.2) and hypoeutectic LM25 (A356) alloys were selected for each step and cast into the steel mold. Thermal analysis technique was used to investigate the solidification behavior of both LM25 and LM28 alloys and to improve the accuracy of TSC process by determining the curves of olid fraction versus time and temperature. It seems that the modified product is obtained by second pouring of LM28 alloy after 30s duration on 39% of solidified LM25 alloy at 602oC. At this situation, a suitable condition has been prepared for Si diffusion at the interface region. The final products were studied through optical microscopy, image analysis and hardness measurement.

Computer simulation of the casting process is becoming and indispensable tool in the effort to achieve high casting yield. In this work, the fluid flow and solidification behavior of a 420 kg weight cylindrical shape casting is studied. Various bottom gating systems were designed and simulated using one of the available simulation software in the foundry market. Results showed less surface turbulence would be realized when metal entrance velocity in the gate was limited below one meter per second. Casting yields were changing between 35 to 40 percent and the best result was obtained in 36 percent.

The influence of the primary silicon phase and of eutectic silicon on the solidification process of hypereutectic Al-15Si alloys with the addition of La and Ce is presented. The microstructures were examined with conventional light microscopy and scanning electron microscopy. The simultaneous refinement of both the primary and the eutectic silicon particles wasn’t achieved with La and Ce additions. It results showed that the addition of lanthanum and cerium doesn’t cause the refinement of the primary silicon grains. While Lanthanum and cerium caused by stress concentration regions. The results showed that the addition of lanthanum and cerium had a negative influence on the alloy’s tensile strength.

Flanges are widely used for connecting valves, pipes and other industrial devices such as gearboxes. Method of producing a flange has a considerable impact on the manner of their involvement with the industrial engines and gearboxes. By Using die casting instead of sand casting and machining for manufacturing flanges, production speed and dimensional accuracy of the parts increases. In this paper, a typical die of an industrial helical gearbox flange (size ISO 50) was designed and die casting process for producing this type of flange was simulated using ProCAST software. The results of simulation were used for optimizing die design. Finally, using the results of the analysis, optimized die was built.

In this study, the analysis of oxygen injected into the molten aluminum has been investigated to produce composites (MMC). Aluminum oxide (Al2O3) is a hard phase in the soft aluminum that acts as the reinforcing phase and has a considerable impact on the mechanical properties of aluminum, especially the wear resistance, hardness and strength properties. Oxygen in molten aluminum at high temperatures leads to the formation of Al2O3. 1 kg of molten aluminum produced at temperatures above 850°C and the oxygen flow rate of 5 liters per minute was injected into molten. To evaluate the effect of oxygen blowing, a sample with argon gas blowing was prepared as a control sample. For samples characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) analysis and various tests hardness, abrasion and tensile standards ASTM, were used to evaluate mechanical properties. Results from this study indicate that with oxygen injection in molten aluminum, the properties such as hardness, tensile strength and wear resistance increases.

In this study, first, the intermetallic compound MgZn2 was produced by melting components under controlled conditions. Then after evaluating the quality of intermetallic, it was milled to covert to powder form. In the next step, it mixed with 2wt. % stearic acid and pure copper powder at weight percent ratio of 3, 5 and 8 separately. The mixture powder was milled for 25 hours by attritor ball milling at ball to powder weight ratio of 10 to 1 to produce Cu-MgZn2 nanocomposite. The X-ray diffraction was used to characterize the structure and the compression test was used to evaluation of mechanical properties .The results show that samples with 3wt.% reinforced of the particles in the samples has better mechanical properties than are others. It was also observed that the electrical resistivity increases with increasing weight percentage of reinforcement.

Silicon nitride coating produced by a double step method used for improvement of wear resistance cold work steel (type D2). silicon coating was produced by pack cementation process and then plasma nitriding process used in second step. For silicon coating by pack cementation method a mixed powder %12Si%0.5NH4Cl.5Al2O3 , temperature 950oC and time 3h used. plasma nitriding was carried in %75 H2 - %25 N2 gas mixture in temperature 550oC and 7h. Coating properties was investigated by Scanning Electron Microscopy (SEM), X-Ray Diffraction analyses (XRD) . nitride phases including β-Si3N4, CrN, Fe4N and Fe3N, and SiCrAl were produced. Wear test showed a significantly improvement of D2 cold work steel by β-Si3N4 and SiCrAl phases.

Aluminum-silicon-copper alloys in most cases are heat treated. The response of these alloys to aging is very slow. In this investigation, to solve this problem, 0.2, 0.4 and 0.7wt% magnesium were added to Al-10Si-3.5Cu alloy. The new alloys were heat treated through two types of precipitation hardening processes with different solution heat treatment stages. The results showed that the presence of different amounts of magnesium in the composition of this alloy extremely accelerates the response to aging treatments and leads to increase the hardness and strength.. Applying two-stage solution heat treatment on new alloys, produced high strength aluminum alloys compared with using single-stage solution heat treatment. The results showed that Al-10Si-3.5Cu alloy containing 0.2% magnesium and heat treated through two-stage solution process, leads to optimum properties having 383.9 MPa ultimate tensile strength, 289.7 MPa yield strength and 3.97% elongation and due to its extraordinary mechanical properties and casting characteristics, can be used as a substitute for a large number of aluminum castings which need high strength.