Study On The Microstructure And Properties Of IF Steel Processed By Friction Stir Processing

Friction stir processing(FSP) is a new method of material modification. Superficial fine grained materials of IF steel were fabricated by FSP, as well as the microstructure and mechanical properties of fine grained material were analyzed based on the optimal FSP parameters. The effect of FSP on the electrochemical corrosion behavior of IF steel in 3.5 wt.% Na Cl solution and 0.9 mmol/L H2SO4 sulution was evaluated. Moreover, neutral salt spray test was also used to assess the corrosion property of the FSPed IF steel. Base on the above researches, the effect of FSP on the mechanical and corrosion properties of fine grained IF steel was summarized. The main results are as follows:Optimal technological parameter of FSP was 950 r/min and 60 mm/min, reduction was 0.2 mm, and FSP experiment was carried out in an argon atmosphere, when the processing was completed, the dry ice alcohol solution was poured into the processing tank quickly to cool. The surface grain size was refined from 45 μm to 2 μm successfully. Compared with BM, the average hardness of SZ and the highest hardness of surface area were increased by 140.8% and 324.8%, the tensile strength of the specimen with surface and the specimen without surface were increased by 150.9% and 147.6%, and the elongation were slightly decreased.In the solution of 0.9 mmol/L H2SO4 and 3.5 wt.%Na Cl, compared with BM, the corrosion potential Ecorr of the fine grain material were improved by 99.37 m V and 64.25 m V, the corrosion current density of the fine grain material were decreased by 47.0% and 32.8%. The film resistance Rr and charge transfer resistance Rct of the FSPed material were improved, and the morphology of surface corrosion was lighter.In the 5wt.%Na Cl neutral salt spray, the average corrosion rate of BM(1.60 g/m2?h) was 1.2 times of the surface material(1.34 g/m2?h), and was 1.3 times of the fine grain material(1.23 g/m2?h). The corrosion degree of the three materials became worse with the time, the degree of surface corrosion was lighter than BM, and these results were in good agreement with the experimental results of electrochemical corrosion. Compared with BM, the corrosion resistances of the FSPed material were obviously improved.