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Zhang R.H.,Jiangsu University | Ma D.X.,Jiangsu University | Sun S.C.,Jiangsu University | Mao J.Z.,Suzhou Mingzhi Technology Company Ltd
Manufacturing and Engineering Technology - Proceedings of the 2014 International Conference on Manufacturing and Engineering Technology, ICMET 2014

Some leakage problems are found in some casting aluminum alloy heat-exchangers which are produced by core assembly molding and low pressure casting during gas tight test. In order to know the reasons that lead to the leakages, the defects and microstructure of the leakage positions are observed by MM6 metallographic microscope and compared with those of sound positions in the same heat exchanger. According to the observation and contradistinction, a consequence was achieved that it is the interaction of shrinkage porosities, gas-shrinkage porosities and microporosities that lead to the leakages. Some control measures are proposed on the base of this consequence to avoid these leakage defects. © 2015 Taylor and Francis Group, London. Source

Zhang Z.-J.,Jiangsu University | Si N.-C.,Jiangsu University | Sun S.-C.,Jiangsu University | Liu G.-L.,Jiangsu University | Wu Q.-F.,Suzhou Mingzhi Technology Company Ltd
Zhongguo Youse Jinshu Xuebao/Chinese Journal of Nonferrous Metals

The casting silumin ZAlSi7Cu4 that was treated with different technologies for heating processing was used to make a thermal cycle experiment at 20↔300°C, 20↔350°C and 20↔400°C, respectively, on a self-restrict thermal fatigue experimental machine. The effect of thermal fatigue property caused by different technologies for heating processing and the effect of crack growth caused by different temperature breadths were studied. Optica1 microscopy (OM) and scanning electron microscopy (SEM) were used to examine the damage mechanisms of thermal fatigue. The results show that the sample with T6 treatment has better property than other two kinds of samples. The expansion path of crack can be influenced by the location of grains. With the increase of the maximum temperature, the lifespan of three kinds of alloys will decrease when the minimum temperature is fixed. In the interval of 300-350°C, the temperature sensitivity of the alloy is higher than that in the interval of 350-400°C when the minimum temperature keeps at 20°C. Source

Zhang Z.,Jiangsu University | Si N.,Jiangsu University | Liu G.,Jiangsu University | Sun S.,Jiangsu University | Wu Q.,Suzhou Mingzhi Technology Company Ltd
Tezhong Zhuzao Ji Youse Hejin/Special Casting and Nonferrous Alloys

The thermal cycling curves of ZAlSi7Cu4 treated by different heat treatment were drawn on a self-restrict thermal fatigue experimental machine at 25-350°C to understand the effect of different heat treatment processes on the thermal fatigue behavior of the alloy. The thermal fatigue mechanism was analyzed by observing thermal fatigue crack morphology of the alloy samples with the help of OM (optical microscope) and SEM (scanning electron microscope). The results show that the sample with T6 heat treatment is superior to one treated by other process in thermal fatigue resistance at 350°C The expansion path of the crack can be controlled by the location of the grain, and the crack generation in the edge of the cavern can be slowed down with a higher curvature radius. The micro-hardness of the sample surface is decreased with the increase of the thermal cycle number, however, the microhardness of the samples treated by T6 and as-cast quenching plus aging has a slightly ascension in the period before the initiation of the crack. Source

Liu G.-L.,Jiangsu University | Si N.-C.,Jiangsu University | Sun S.-C.,Jiangsu University | Wu Q.-F.,Suzhou Mingzhi Technology Company Ltd
Transactions of Nonferrous Metals Society of China (English Edition)

Al-7.5Si-4Cu cast alloy melt modified by Al-5Ti-B, RE and Al-10Sr master alloys were poured in the chromite sand moulds, to investigate comparatively the effects of individual or combined additions of grain refiners and modifiers on the mechanical properties, microstructures, grain refining and modification, and intermetallic compounds of the alloy. The results show that the mechanical properties and the microstructures of Al-7.5Si-4Cu cast alloys are improved immensely by combining addition of 0.8%Al-5Ti-B, 0.1%RE and 0.1%Al-10Sr grain refiners and modifiers compared with the individual addition and cast conditions. For individual addition condition, addition of 0.8% Al-5Ti-B master alloy can obtain superior tensile strength, Brinell hardness and finer equiaxed α(Al) dendrites. The alloy with 0.1% RE master alloy shows the highest improvement in ductility because the rare earth can purify the molten metal and change the shape of intermetallic compounds. While the alloy with 0.1% Al-10Sr modifier shows only good improvement in yield strength, and the improvement of other performance is unsatisfactory. The Al-10Sr modifier has a significant metamorphism for the eutectic silicon, but will make the gas content in the aluminum alloy melt increase to form serious columnar grain structures. The effects of grain refining and modification on mean area and aspect ratio have the same conclusions obtained in the mechanical properties and the microstructures analyses. © 2014 The Nonferrous Metals Society of China. Source

Wang W.-H.,Jiangsu University | Si N.-C.,Jiangsu University | Liu G.-L.,Jiangsu University | Wu Q.-F.,Suzhou Mingzhi Technology Company Ltd

In order to study the influence of heat treatments on the comprehensive mechanical properties of multiple Al-Si alloy, the alloy specimens in the state of as-cast, water quenching+aging treatment and aging treatment, were carried out in testing machine of 3000 kN, the microstructures of the alloy were analyzed by the optical microscope and SEM, then the mechanical properties were tested. The results show that, the mechanical property of the multi-component Al-Si alloy treated by as-cast water quenching+aging is the best among the three states, and then the aging treatment, the mechanical property of as-cast is the worst. For as-cast water quenching is equivalent to a transient solution treatment, dispersed phases (Al 2Cu, Mg 2Si and θ′ phases etc.) would integrate into α solid solution in the solution treatment, then separated out in the aging treatment, which drastically improved the mechanical properties of the alloy. Source

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