Preparation Of Aluminum Alloy Micro-arc Oxidation Composite Coating And Tribological Properties

High-silicon aluminum alloy(ZL109)used as piston manufacturing material has the characteristics of light weight,high specific strength,good thermal conductivity,and low coefficient of thermal expansion.However,its low hardness and lively chemical properties are prone to scratches and corrosion,which limits its operational performance.Therefore,this paper will make a ceramic film layer in situ on the surface of the aluminum alloy by micro-arc oxidation technology.The increase in hardness and the presence of dense layer improve the wear resistance and corrosion resistance of the base material.However,the higher roughness surface of the ceramic film layer shows a high friction coefficient and aggravates the wear between friction pairs,especially under dry friction conditions.So,to further improve its anti-friction performance solid lubrication technologies were performed on the ceramic film layer to prepare a low shear soft composite coating.The specific research contents were developed from the following aspects:(1)The control and optimization of the micro-arc oxidation process parameters.First,the growth rate of the film layer was studied with the oxidation time,and then,the forward voltage phase adjustment was carried out.These aimed to prepare a film layer with a larger proportion of dense layers and a higher hardness as the carrier substrate.(2)In order to improve the anti-friction performance of the ceramic film,P-MAO coating was prepared by fine polishing treatment,P-MAO-W and MAO-W coatings were prepared by throwing WS2 powder;ceramic-based polyimide organic composite coating MAO/PI and lubricant-doped MAO/(PI+WS2)composite coating were prepared by spin coating process..The self-generated discharge channels,cracks,and uneven structures on the surface of the film are used as lubricant texture reservoirs,and the mechanical locking effect is strengthened to prepare a solid lubricating composite coating.And through EDS,SEM/BSE,XRD,imageJ,roughness tester,thickness tester,Vickers hardness tester,reciprocating friction and wear tester,etc.,the microstructure,composition and tribology of ceramic film and composite coating Performance testing.The experimental results show that:(1)During the oxidation time of 0-60min,the thickness and roughness of the ceramic film gradually increase,but the growth rate of the film gradually slows down,and the maximum increase in roughness occurs within the time period of 10-20min;The proportion of dense layer and the porosity of the film layer increase firstly and then decrease.The maximum proportion of the dense layer is about 5/8 at 40min,and the maximum porosity is about 22.8%at 30min;the main component of the layer is ?-Al2O3 In the later period,the components of ?-Al2O3 and mullite gradually increased.(2)In the staged control study,the significant degree of influence on the thickness of the film layer is in the following order:the second stage,the first stage,the third stage.When the electrical parameters of 460-420-380V are used,the film thickness reaches about 70?m.Compared with the single parameter of 420V,it is increased by about 10?m.At the same time,it is found that the ratio of the positive and negative phase voltages affects the transition of the discharge mode.(3)After the ceramic film layer is finely polished or coated with nano-lubricating particles to form a polished film,the surface roughness of the coating can be significantly reduced(from 3.5 ?m of MAO to 0.44?m of P-MAO-W).It can effectively reduce friction coefficient and the wear of coupling pair.The friction coefficient of the MAO group quickly rose to 1.2 within 2 minutes,while MAO-W and P-MAO-W stabilized at about 0.25 and 0.07 for a long time.(4)MAO/PI and MAO/(PI+WS2)composite coatings effectively reduce the friction and wear between friction pairs and extend the failure time of the coating.The friction coefficient of MAO/(PI+WS2)coating is about 0.4%,which is lower than MAO coating by about 50%.The wear quality of MAO/(PI+WS2)coating on cast iron pins is about 0.4mg,which is about 10 times lower than that of MAO coating.The failure loading of MAO/(PI+WS2)coating and lasting time are 70N and 35min,respectively,which are 2.3 times and 2.7 times of the MAO film layer.The load-bearing capacity and anti-sticking performance also have been greatly improved.