Wang Meng, Pang Jianchao, Liu Xinfeng, Wang Jianqiu, Liu Yongquan, Li Shouxin, Zhang Zhefeng
Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China.
Institute of Corrosion Science and Technology, Guangzhou 510530, China.
Materials (Basel). 2022 Oct 13;15(20):7113. doi: 10.3390/ma15207113.
The eutectic cast Al-Si alloys with excellent high-temperature and casting performance are widely used in engine pistons. During frequent starts and stops, the thermo-mechanical fatigue (TMF) is the most important failure cause. Ultrasonic melt treatment (UT) was chosen to compare and investigate the influence of micro-structures on fatigue life and damage mechanisms of as-cast (AC) eutectic Al-Si alloys under TMF loading. After UT, the grain size, primary Si, and intermetallic particles are reduced significantly in the alloy; fatigue life increases obviously. As a result of pilling-up of dislocations, the competitive effects of the critical strain/stress for fatigue crack nucleation can be found. There are two different crack initiation mechanisms under TMF: one is primary Si fracture for AC alloys with limited critical strain/stress for fatigue crack nucleation at fractured Si particles, and the other is primary Si debonding for UT alloys with increasing critical fracture strain/stress. After the crack initiation, the fractured or debonded primary phases provide the advantages for the further development of main cracks for both alloys. The UT alloy (805 ± 253 cycles) has about twice the TMF life of the AC alloy (403 ± 98 cycles). The refinement of micro-structures is instrumental in improving the fatigue resistance and life of TMF for the UT alloy.
具有优异高温性能和铸造性能的共晶铸造铝硅合金广泛应用于发动机活塞。在频繁启停过程中，热机械疲劳（TMF）是最重要的失效原因。选择超声熔体处理（UT）来比较和研究微观结构对铸态（AC）共晶铝硅合金在TMF载荷下疲劳寿命和损伤机制的影响。经过UT处理后，合金中的晶粒尺寸、初生硅和金属间化合物颗粒显著减小；疲劳寿命明显增加。由于位错的堆积，可以发现疲劳裂纹萌生的临界应变/应力的竞争效应。在TMF下有两种不同的裂纹萌生机制：一种是对于在断裂硅颗粒处疲劳裂纹萌生的临界应变/应力有限的AC合金，其裂纹萌生机制为初生硅断裂；另一种是对于临界断裂应变/应力增加的UT合金，其裂纹萌生机制为初生硅脱粘。裂纹萌生后，断裂或脱粘的初生相为两种合金主裂纹的进一步扩展提供了条件。UT合金（805±253次循环）的TMF寿命约为AC合金（403±98次循环）的两倍。微观结构的细化有助于提高UT合金的抗疲劳性能和TMF寿命。
