Study On The Integrated Process Of Casting-Surface Alloying On Cast Aluminum Alloy 48000

Cast aluminum alloys are widely used in engineering and daily life because of high strength,easy processing,low density,high electrical conductivity and thermal conductivity.At the same time,cast aluminum alloy can produce a thin layer of Al₂O₃ oxide film on the surface in the natural environment,making it has a good corrosion resistance in the neutral medium environment.However,Cast aluminum alloys will cause serious corrosion in the deviation from the neutral atmosphere or sea water.Therefore,in order to improve its corrosion resistance,extend the service life,it is necessary to perform the surface treatment of the cast aluminum alloys according to the environment of use.In this paper,combined the casting process and surface treatment technology,the surface treatment of cast aluminum 48000 was carried out by Casting-Surface alloying process through brushing reactive coating in the cavity wall.The effects of the amount of oxidant in the coating,the amount of aggregate,the size of aggregate,the type of aggregate and molten salt on the casting-surface alloying process were studied.The properties of the alloying layer such as thickness,composition,corrosion resistance were tested.And explored the formation process and mechanism of the alloying layer.The results show that it can be formed an alloying layer with thickness of about 2?4 u m on the surface of cast aluminum 48000 by using casting-surface alloying process.With the increase of the CrO₃,the thickness of the alloying layer are increased,but when the amount of CrO₃ is too much,the surface quality of the casting will be depressed.When the relative content of aggregate is less,the sticky on the casting surface is serious,however when the relative content of aggregate is increased,there is obvious brush mark on the casting surface.When the aggregate size is relatively large,the casting surface will have a lot of small pits,alloying layer surface delamination phenomenon,aggregate size is too small,the alloying layer is thin.Adding molten salt to the coating increases the slag on the surface of the casting;The use of double-layer paint,casting quality improved significantly,has smooth surface,the alloying layer is uniform and dense.The thickness of alloying layer prepared by SiC,SiO₂,Cr2O₃ and Fe2O₃ is uniform.The alloying layer of SiO₂ is the thickest,about 3?m,and the rest is about2 ?m.The composition of the alloying layer is Al,Si,O,Cr,indicating that the constituent materials of alloying layer mainly are alumina oxide,chromium oxide and silicon oxide.lt is found that the microstructure of the castings with SiC and SiO₂ is smooth and compact,and the microstructure of the castings with Cr2O₃ and Fe2O₃ has a lot of stripe or gully.Spherical Al₂O₃ is formed on the four sample surfaces.The corrosion resistance of samples of different kinds of aggregates in 3.5%NaCl solution was studied using weight loss method and electrochemical impedance method.It is found that the corrosion resistance of the samples after alloying treatment was improved obviously.Samples that did not do any treatment had etched corrosion after 360 hours of corrosion,and the treated samples had pitting corrosion.