| Al alloys have high ratio of strength/density and widely used in the fields of aircraft industry and other industries. However, because its low surface hardness and relatively poor pitting resistance, it is very important for Al alloys to improve corrosion resistance and wear resistance by use of surface modification technology.Compared with the traditional ion implantation, the plasma-enhanced ion beam technology not only can treat a complex-shape component, but also combines the material surface preparation/cleaning and modification stages in a single-step process. Material surfaces are subjected to preparation (including heating, degassing and cleaning), rapid melting and cooling processes continuously. This technology is simple and low-cost. It is different from ion implantation. Energy is deposited on the material surfaces during the ion beam bombardment without change of chemical composition. It is a promising technology in surface modification of materials.In this investigation, the widely used 2024A1 and 7075A1 alloy samples were selected and the sample surfaces were modified by use of plasma-enhanced ion beams. In compare with non-treated samples, the characteristic surface morphology and microstructure change of the samples treated by plasma-enhanced ion beams was observed. Their tensile strength and bending fatigue properties were tested. The interaction between ion beam and sample surface was studied. The electrochemical behavior of ion beam treated samples was analyzed and the anodic polarization curves were obtained. The corrosion potentials and corrosion current density was determined. The fatigue behavior of the ion beam treated samples in corrosive environment. In this case, the effects of pre-fatigue test on electrochemical corrosion resistance of samples, the effects of pre-corrosion on fatigue properties of samples and the effects of ion beam treatment on corrosion fatigue properties of samples were investigated. The corrosion fatigue life of samples was determined and models of corrosion fatigue life analysis foe Al alloys were discussed.With the results of this investigation, the following conclusions may be obtained.1. With treated by plasma-enhanced ion beams, distinct changes in surface morphology of samples were observed and various forms of craters, cones, depressions, ridges, trenches or blisters were produced on the ion beam treated surfaces of samples.2. The surface melting and rapidly cooling took place on the surface layer ofsamples treated by plasma-enhanced ion beams. In this study, the required minimum energy density for the melting of surface layer of Al alloy sample is in the range of 1.2-1.6 J/cm2, corresponding to an ion beam energy of 200 keV, current density of 60-80 A/cm2, and pulse duration time of 10-9 seconds.3. The plasma-enhanced ion beam treatment produced little influence on the tensile strength, elongation and bending fatigue strength of samples in air.4. The corrosion resistance of Al alloy samples was improved significantly by ion beam treatment. The corrosion current density measured from ion beam treated samples was much lower than that of non-treated samples. Based on the values of relative corrosion rate calculated from corrosion current density, the corrosion resistance increased by 56-89% for treated 2024 Al alloy samples, and 55-78% for treated 7075 Al alloy samples respectively.5. The anodic current density was increased for both treated samples and non-treated samples, when pre-fatigue test was performed before corrosion tests. However, under the same condition, the measured anodic current density from treated samples was distinctly lower than that from non-treated samples.6. The immersion corrosion performed before fatigue tests greatly reduced the fatigue life of samples. Compared to the fatigue life of samples without pre-corrosion, the fatigue life was reduced by 30-40% for treated samples and almost one magnitude for non-treated samples.7. Compared with the fatigue properties of samples in air, the...
|
PDF Full Text Request