汽车发动机用A356合金的热疲劳行为

Thermal Fatigue Behavior of A356 Alloy for Automotive Engine

研究了温度幅分别为25~300℃、25~350℃和25~400℃时,铸态A356合金、细化变质A356合金、微合金化A356合金和T6态微合金化A356合金的热疲劳行为;分析了热裂纹萌生和生长的机理。结果表明,在相同温度幅下,热疲劳裂纹萌生寿命从大至小的顺序为:T6态微合金化A356合金、微合金化A356合金、细化变质A356合金、铸态A356合金;在热疲劳裂纹形成后,裂纹扩展早期阶段的裂纹生长速度要高于扩展后期;铸态A356合金和细化变质A356合金的热疲劳裂纹呈弯曲状且主要以沿晶方式扩展;微合金化A356合金和T6态微合金化A356合金的热疲劳裂纹更加平直和细小,且以穿晶-沿晶的混合方式扩展;T6态微合金化A356合金具有最佳的抗热疲劳性能。

The thermal fatigue behavior of as cast A356 alloy, refined modification A356 alloy, microalloyed A356 alloy and T6 mieroalloyed A356 alloy at temperature range of 25-300 ℃, 25-350℃and 25-400 ℃ were investigated, and the mechanism of thermal crack initiation and growth was analyzed. The results show that at the same temperature range, the thermal fatigue crack initiation life from large to small order is： T6 microalloyed A356 alloy, microalloyed A356 alloy, refined modification A356 alloy and as cast A356 alloy. The crack growth rate in the early stage of crack propagation is higher than that of later stage after thermal fatigue crack formation. The thermal fatigue cracks of as cast A356 alloy and refined modification A356 alloy are curved and expands mainly along the grain boundary. The thermal fatigue cracks ofmicroalloy A356 alloy and T6 microalloyed A356 alloy are more straight and small, which extends in the mixing mode of transgranular-intergranular form. T6 rnicroalloyed A356 alloy has the best thermal fatigue resistance.