Study On The Process Of Micro-arc Oxidation On Hot-dip Aluminized Surface On 304 Hot-rolled Stainless Steel

In this paper, hot-dip aluminized and micro-arc oxidation technology were used on 304 hot-rolled stainless steel to prepare a layer of oxide ceramic membrane in order to improve the ability of its corrosion resistance to molten aluminum liquid. Conducting the test by changing fluxing agent, dipping time and plating bath temperature and then observing the cross-section microstructure of the sample and measuring the pure aluminum and alloy layer thickness to get the best hot-dip aluminized technological parameters suitable for later micro-arc oxidation. And then the effects of current density, oxidation time, pulse frequency and duty cycle on the thickness, surface roughness and surface microstructure were investigated by eddy current thickness gauge, surface roughness measuring instrument and SEM. Study on the stainless steel substrate and ceramic membrane’s corrosion resistance to molten aluminum liquid was conducted by high temperature molten aluminum etching test. The results showed that:The optimal technological parameter of 304 hot-rolled stainless steel hot-dip aluminized is: using 20g/L AlF3 solution as fluxing agent, dipping 15 min at 750℃. Using the optimal technological parameter obtained sample’s surface is compact without defects, in the cross-section between the pure aluminum layer and the alloy layer and between the alloy layer and the substrate microstructure are all metallurgical combination, closely combined. The pure aluminum layer thickness is 225 μm, the alloy layer thickness is 25 μm. The thickness is beneficial to the following micro-arc oxidation test.In the electrolyte formula of Na₂SiO₃ 10g/L+KOH 2g/L, the optimal process parameters: current density is 20 A/dm2, oxidation time is 30 min, pulse frequency is 50 Hz, and duty cycle is 40 %. The porous structure of the ceramic layer surface can be found by scanning electron microscope. Sintered micro porous homogeneous and dense, showed a volcano shape. Between the ceramic layer and the substrate is metallurgical combination, the sample surface is continuously and completely covered by the ceramic layer. By XRD test, we know that the main component of ceramic layer are Al, α- A1₂O₃ and γ- A1₂O₃. The sample of 304 hot-rolled stainless steel without any treatment and the sample after micro-arc oxidation process conduct the high temperature aluminum liquid corrosion test at the same time, the sample without any treatment corrosion is serious, the dimension of the width and thickness decreased significantly; the sample after micro-arc oxidation treatment was not obvious corrosion, after the erosion test, the ceramic layer remains intact and continuous. Therefore, the sample after micro-arc oxidation treatment has good resistance to molten aluminum corrosion performance.