The Research On Preparation And Thermal Shock Resistance Of Micro-plasma Oxidation Layer On Aluminum Alloy

Aluminum and its alloys are widely used in many application fields due to their excellent mechanical and physical properties such as higher specific strength, excellent electrical conductivity, thermal conductivity, easily forming and machining, etc. However, its lower high-temperature strength and poor corrosion resistance confine its applied range, especially in high temperature environment.If a ceramic layer which possesses of good thermal shock resistance can be prepared on the surface of aluminum alloy, it can solve this problem and extend the application fields of aluminum alloy.Micro-plasma oxidation (MPO) is a new surface modification technology, which can form the ceramic coatings in-situ on the surfaces of some non-ferrous metals such as Al, Mg and Ti and its alloys etc. It happened to salve this problem.Firstly, electrolyte solution system was optimized by orthogonal tests in this paper. Secondly, the current density and oxidation time effect on growth speed of MPO ceramic layer were studied. At last, the formation mechanism, structure and morphology of ceramic layer were researched as well as.Thermal shock resistance is one of the most important indexes of MPO ceramic layer. The experiment of thermal shock resistance was investigated by heating-quenching method. The results show as follows: (1) MPO ceramic layer has a good thermal shock resistance, adhesion strength to the substrate as well as. (2) With the increase of current density, the capability of thermal shock resistance of ceramic layer decrease. The suitable rang of current density is 3-7A/dm2. (3) The failure modes of MPO ceramic layer in thermal shock experiment shows that firstly the loose layer is stripped from ceramic layer, and then dense layer stripped from the aluminum alloy substrate. (4) The thermal shock resistance must have decreased if the ceramic layer is too thick or thin.Thermal conductivity plane model of MPO ceramic layer piston is modeled to estimate the thermal shock resistance in this paper. The results show as follows: (1) Theoretical analysis shows that relation between temperature gradient and environment temperature difference is a near-linear. (2) Generally, MPO ceramic layer which possesses of low thermal conductive coefficient have not good thermal rock resistance. (3) The reasonable thickness of ceramic layer is in range of 20-30μm. And this range will decrease with the current density increase.