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2 Archives of Foundry Engineering

2 2021

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Creep Behaviors at 275°C for Aluminum-Matrix Nano-composite under Different Stress Levels

Azadi M., Behmanesh A., Aroo H.

Archives of Foundry Engineering

2021

Vol. 21, iss. 3

81--89

Aluminum alloys, due to appropriate strength to weight ratio, are widely used in various industries, including automotive engines. This type of structures, due to high-temperature operations, are affected by the creep phenomenon; thus, the limited lifetime is expected for them. Therefore, in designing these types of parts, it is necessary to have sufficient information about the creep behavior and the material strength. One way to improve the properties is to add nanoparticles and fabricate a metal-based nano-composite. In the present research, failure mechanisms and creep properties of piston aluminum alloys were experimentally studied. In experiments, working conditions of combustion engine pistons were simulated. The material was composed of the aluminum matrix, which was reinforced by silicon oxide nanoparticles. The stir-casting method was used to produce the nano-composite by aluminum alloys and 1 wt.% of nanoparticles. The extraordinary model included the relationships between the stress and the temperature on the strain rate and the creep lifetime, as well as various theories such as the regression model. For this purpose, the creep test was performed on the standard sample at different stress levels and a specific temperature of 275 oC. By plotting strain-time and strain rate-time curves, it was found that the creep lifetime decreased by increasing stress levels from 75 MPa to 125 MPa. Moreover, by comparing the creep test results of nanoparticle-reinforced alloys and nanoparticle-free alloys, 40% fall was observed in the reinforced material lifetime under 75 MPa. An increase in the strain rate was also seen under the mentioned stress. It is noteworthy that under 125 MPa, the creep lifetime and the strain rate of the reinforced alloy increased and decreased, respectively, compared to the piston alloy. Finally, by analyzing output data by the Minitab software, the sensitivity of the results to input parameters was investigated.

Comparing of High-Cycle Fatigue Lifetimes in Un-corroded and Corroded Piston Aluminum Alloys in Diesel Engine Applications

Azadi M., Aroo H., Azadi M., Parast M. S. A.

Archives of Foundry Engineering

2021

Vol. 21, iss. 1

89--94

Diesel engine components in the combustion chamber have been exposed to cyclic loadings under environmental effects, including high temperatures and corrosive fluids. Therefore, knowing the corrosion-fatigue behavior of materials is essential for designer engineers. In this article, pure fatigue and corrosion-fatigue behaviors of the piston aluminum alloy have been experimentally investigated. For such an objective, as-cast and pre-corrosive standard samples were tested by the rotary bending fatigue machine, under 4 stress levels. Some specimens were exposed to the corrosive fluid with 0.00235 % of the sulfuric acid for 100 and 200 hours. The results showed higher weight losses for 200 hours immersion times. As another result, it could be concluded that the lifetime decreased in pre-corrosive samples for both 100 and 200 hours of the immersion time, compared to that of as-cast specimens. However, such a lifetime reduction was more significant for 200 hours of the immersion time, especially within the high-cycle fatigue regime (or lower stress levels). Under high stress levels, both pre-corrosive sample types had almost similar behaviors. The field-emission scanning electron microscopy images of specimen fracture surfaces indicated that the brittle region of the fractured surface was larger for specimens after the 200 hours of corrosion-fatigue testing than the other specimen.