The normal T6 heat treatment process for cast A356 alloy generally requires about 15 h. This longperiod procedure increases greatly the manufacturing cost and decreases the productivity in practical production. In thi...The normal T6 heat treatment process for cast A356 alloy generally requires about 15 h. This longperiod procedure increases greatly the manufacturing cost and decreases the productivity in practical production. In this study, a new short-time heat treatment process with only 30 min solution time at 540℃ was developed for the production of motorcycle wheel hubs in order to reduce heat treatment time. Comparisons on microstructure evaluation and mechanical properties, such as tensile strength and ductility, were made between this new fast process and the conventional T6 heat treatment. The results revealed that this new heat treatment process enabled the spheroidization of the eutectic silicon thoroughly, while minimizing the growth of eutectic silicon. The A356 alloy after this new short-time heat treatment shows nearly equal mechanical properties compared with the same alloy heat treated in a normal T6 heat treatment. This investigation makes it possible to significantly improve the efficiency of heat treatment on A356 alloy and, at the same time, improve the mechanical properties of the alloy.展开更多
【目的】通过比较两种不同杀菌处理(高温短时High temperature short-time和超高压Ultra-high pressure杀菌)的非浓缩还原(Not from concentrate,NFC)苹果汁贮藏期品质变化,为我国NFC果汁产品标准的制定和规范市场NFC果汁产品货架期提...【目的】通过比较两种不同杀菌处理(高温短时High temperature short-time和超高压Ultra-high pressure杀菌)的非浓缩还原(Not from concentrate,NFC)苹果汁贮藏期品质变化,为我国NFC果汁产品标准的制定和规范市场NFC果汁产品货架期提供试验依据。【方法】以‘红富士’苹果为原料制备NFC苹果汁,采用高温短时杀菌(HTST,98℃,50 s)和超高压杀菌(UHP,400 MPa,15 min)处理后,在4℃条件下冷藏,利用微生物学、化学及主成分分析(PCA)等方法以及HPLC、GC-MS等手段研究两种不同杀菌处理的NFC苹果汁贮藏期微生物、理化指标、多酚含量、酶(Polyphenol oxidase,PPO;Peroxidase,POD)活性、抗氧化活性、香气成分的变化。【结果】HTST和UHP处理对细菌总数、大肠杆菌、霉菌与酵母的杀菌率均为100%,但贮藏第10、5周时果汁菌落总数分别呈显著增加(89.15%、58.65%),大肠杆菌、霉菌与酵母增殖速度不明显;贮藏期HTST和UHP两种处理NFC苹果汁微生物种群变化小,但优势菌属不同。两种处理的NFC苹果汁贮藏期可溶性固形物、pH、总酸的变化不大,但总色差显著增大(P<0.05);贮藏期HTST和UHP处理NFC苹果汁中表儿茶素分别下降了33%和53%,FRAP总抗氧化能力和DPPH自由基清除率分别保持在76%、73%和77%、76%,HTST处理NFC苹果汁的多酚含量和抗氧化活性明显高于UHP处理的样品;HTST处理后贮藏期NFC苹果汁的PPO与POD完全失活,但UHP处理样品的酶活性呈现先增大后降低的趋势。HTST处理后果汁18种特征香味物质总的保留率为52%,但贮藏期香气成分保持稳定;UHP处理NFC苹果汁的香气含量(57.75 mg/100 mL)接近对照样品(57.17 mg/100 mL),但贮藏期香气成分变化显著,降低了26.13%。【结论】HTST和UHP杀菌处理的NFC苹果汁在4℃可分别贮藏9、4周,贮藏期内其品质满足商业要求,HTST处理NFC苹果汁货架期长于UHP处理。展开更多
基金financially supported by the National Natural Science Foundation of China under project 51574129
文摘The normal T6 heat treatment process for cast A356 alloy generally requires about 15 h. This longperiod procedure increases greatly the manufacturing cost and decreases the productivity in practical production. In this study, a new short-time heat treatment process with only 30 min solution time at 540℃ was developed for the production of motorcycle wheel hubs in order to reduce heat treatment time. Comparisons on microstructure evaluation and mechanical properties, such as tensile strength and ductility, were made between this new fast process and the conventional T6 heat treatment. The results revealed that this new heat treatment process enabled the spheroidization of the eutectic silicon thoroughly, while minimizing the growth of eutectic silicon. The A356 alloy after this new short-time heat treatment shows nearly equal mechanical properties compared with the same alloy heat treated in a normal T6 heat treatment. This investigation makes it possible to significantly improve the efficiency of heat treatment on A356 alloy and, at the same time, improve the mechanical properties of the alloy.
