Mechanical Properties Of Function Gradient Films On Magnesium Alloy

Magnesium alloys has been considered as the most promising green engineeringmaterials in the21st century, but the problems of wear, corrosion and dynamic wear-corrosion synergy failure existing in the current parts limits its application. In order tosolve the problem, a new method of the functional composite films system consisting ofthe substrate bonding layer and the corrosion insulation layer and the middle bearing layerand the top wear-resisting layer is proposed in this study. Numerical simulation andexperiment were used to determine the mechanical property of the system. The researchresults will provide theoretical understanding and technique support for design andsynthesis of the functional gradient films. It has practical significance for industrialapplication of magnesium alloy parts.First of all, geometrical model of nanoindentation process and micropillarcompression test of multilayers and substrate system was build. Finite element methodwas used to compute and analyze all the processes. Elastic modulus and the hardness ofsubstrate were determined, which is compared with the instrumented indentation, thedifference of simulation and experiment was negligible. The evolution law of the internalstress and strain field of the system was also predicted. Micrompression test of substratewith different diameters under the flat tip show that the flow stress increases withdecreasing pillar diameter. The size effect of pillar is obvious.Secondly, to obtain the properties of the breakdown structures, particular simulationsand analysis of nanoindentation were carried out. The hardness and load capacity ofcoated magnesium alloy was13and10times larger than the uncoated substrate. Functiongradient films absorbed most of the energy during the process of indentation, the substratewas proceeded effectively. Due to the influence of the substrate, the result of simulationand experiment both show distinct size effect.Thirdly, simulation and analysis of micro compression test of functional compositefilms pillar was also executed. The results show that the stress-strain response ofmicropillarimplies“smallerisstronger”,duetodifferencesofthedislocation distribution.Pillars either with square cross section or no-substrate show similar stress-strain responsecompared with micro cylindrical pillar. Strain concentration exist at AlN/CrAlN interfacein micro square pillar. Flow stress increases and the distribution of stress is moreconcentrated in the no-substrate pillar.Finally, based on the composite processing technology, functional composite filmssystem was fabricates on the magnesium alloy surface, then given testing and analysis.The results show that thin films prepared by the composite processing technique complywith the design requirements. Besides the relationship among the composition, structure, load capacity and deformation was revealed. The nanoindentation and micropillarcompression experiments provide elastic modulus, hardness value, and residualdeformation after unloading, compressive strength and yield strength of the system. Thecorrectness of simulation are proved by comparing the experiment and simulation.