Study Of Fatigue Properties Of 7A04 Aluminum Component And Anodizing Standard Samples

In recent years, with the development of Chinese railway industry, Speed and load requirements have been increasingly high, the same with the requirements of fatigue design of component. As an important structural component of Bogie, traction beam is also faced with the same situation. Furthermore, the operating environment of EMU is very complex, and corrosion medium has a great impact on the performance of aluminum, and the corrosion fatigue is also another serious problem to traction beam. On these issues, the performance of 7A04 aluminum alloy was studied in this paper from two aspects.(1) Based on the finite element calculation, fatigue strength of aluminum traction beam in service conditions was calculated by the application of the nominal stress method. The results showed that, the traction beam didn’t fail due to fatigue fracture when the cycles of cyclic loading was up to ten million times. The acceleration test was designed based on the method of linear enhancement load. Under the condition of five times the actual load, the calculated fatigue life with FE-SAFE software was 352604 cycles, and the measured fatigue life was 389417 cycles. Fracture location was identical with the maximum stress in finite element predicting.(2) The influence of anodizing on the pre-corrosion fatigue performance of 7A04 aluminum alloy was studied. The smooth specimen and the specimen through the treatment of oxalic acid anodizing were corroded for 1 hour in denudation liquid. The fatigue limit was tested on fatigue testing machine GPS-100 on the smooth specimens, anodized samples, pre-corrosion smooth specimens, pre-corrosion anodized sample. Fatigue fracture mechanism was studied through the observation of fracture surface. Contrasting smooth specimens and anodized samples found that fatigue limit after being anodized decreased by 36.8%. After 1h of pre-corrosion, smooth specimens and anodized samples fatigue limit were 229.33MPa and 236.67MPa respectively, so anodizing and pre-corrosion treatments resulted in the reduction of the fatigue limit of 7A04 aluminum. Under the same corrosion conditions, anodizing treatments will improve fatigue strength of 7A04 aluminum alloy. It was found that secondary phase had a significant impact on fatigue strength by fracture surface observation. Secondary phases not only made corrosion easier, but also made the pores of the anodic oxide film unevenly distributed. Anions was easier to enter into the bottom of the pores of the anodic oxide film when subjected to corroding, and the anions damaged the integrity of the anodized film, so that the fatigue properties of the material decreased.