Several techniques have been employed in the alloy application. However, surface mechanical attrition treatment (SMAT) have remained dominant due to its advantages. It is good at enhancing properties of the material such as fatigue resistance, ductility, diffusion rate and reduced friction and wear. Additionally, the relationship between the fatigue and corrosion properties of an alloy is very vital in understanding their performances. Ultrasonic shot peening (USSP), though considered as a method of SMAT is regarded as a simplification of the high performing metals composition due to their effectiveness. USSP is very significant in evaluating the effects of corrosion and energy on the behavior of materials such as the AA7150.
Researchers at Purdue University in the United States and led by Professor Qingyou Han in collaboration with Dr. Jie Li at Central South University in China studied the impact of the ultrasonic shot peening on the behavior of the AA7150 material. Also, the study also compared the relationship between the corrosion properties and the induced energy for both treated and untreated alloys materials and how they influence other essential properties and parameters of the same material. Their research work is currently published in the journal, Corrosion Science.
The authors prepared their experiment by using T7751 aging treated 7150 aluminum alloys. After the AA7150 was cut into the required experimental dimensions and grounded, ultrasonic shot peening treatment then followed. To evaluate the impact of the applied energies, the USSP treated specimen was characterized in four parameters namely peening distance, the diameter of the ball used in the experiment, amplitude and the peening time.
The authors successfully observed that for the USSP treated low energy peened specimen, needle-like pits having deeper depths. When compared to the untreated alloys, it was observed that the depth was deeper and the sample also retained its localized corrosion properties. On the other hand, high energy pinned alloys produced the opposite results. For instance, they lost their localized corrosion properties and never produced as deep penetration depth as in the case of those of low energy.
They investigated most of the ignored areas in the past study of corrosion such as galvanic interaction, localized corrosion nature and the measurement of the obtained corrosion depths. This led to an establishment of a more reasonable relationship between the localized corrosion kinetics, the material surface composition as well as the galvanic interaction properties. For instance, an increase in the pit initiation resistance and the decrease in the propagation kinetics are obtained when nanograins are formed on the surface of the AA7150 material. This was however influenced by the pit morphology that depends on the gradient microstructure. According to the authors, two significant factors affect the localized corrosion of USSP treated AA7150, and that is, propagation kinetics together with pit initiation.
Sun, Q., Han, Q., Xu, R., Zhao, K., & Li, J. (2018). Localized corrosion behavior of AA7150 after ultrasonic shot peening: Corrosion depth vs. impact energy. Corrosion Science, 130, 218-230.