Research On A New Kind Of Low Pressure Casting Coating For Aluminum Alloy

Aluminum alloy as ideal lightweight structural materials is widely used in automobiles, motorcycles, internal combustion engine, electronics, aerospace and instrumentation industries for its high specific strength and good processing properties. As one of the most commonly used of daily production of aluminum alloy castings, low pressure casting method has the advantages of high precision casting and good internal quality.The coating is one of the key technologies to make sure the quality of castings.This article is in view of the low pressure casting of aluminum alloy wheel hub process and focus on developing an new kind of low pressure casting metal mold coating for aluminum alloy, used to solve the problem of break off easily and poor surface of coating.First is to choose a kind of inorganic material as refractory aggregate for the good lubrication performance with layered structure of hexagonal, and select Si-Al-Cr ternary composite sol as the binder prepared by sol-gel method. By using a variety of additives and fully mixing and grinding, the basic coating is prepared.The add amount of refractory aggregate and spraying process parameters on the coating performance and the influence of the morphology were studied.Refractory aggregate studies show that when adding amount was 15%, the metal substrate preheating temperature is 250 ?, spraying distance is 90 cm, the coating surface were smooth and the surface quality of the best, the coating bond strength reached level III.Secondly, the paper studied the effect of phosphate binder on the coating performance, through SEM, EDS and differential thermal analysis method analyzed the morphology and structure of the coating and the formation mechanism.With the increase of phosphate binder adding proportion, the density and viscosity value of coating falled, And the suspension rate of coatings shows ascendant trend, the coating bond strength reach class II.When Si-Al-Cr ternary composite sol and phosphate binder adding proportion was 5:2, after heat treatment crack on the surface of coating was less, and the heat loss of quality was minimum. Also the adhesion of the coating and the magnesium substrate was 165.4 N/cm2, coating and the substrate bonding strength and thermal shock performance achieved the optimal.At the same time, the XRD spectrum analysis showed that the coating produced new phases like Fe4(PO4)3(OH) 3, Al80Cr13.5Fe6.5, Al0.7Fe3Si0., AlPO4 etc. It shows that the complex binder makes full use of bonding strength of the sol at low temperature and phosphate at high temperature performance, the combination of composite binder makes up for the deficiency of the single binder. The solidification process is beneficial to the formation of macromolecular network to improve the coating adhesion effectively.Finally, Through actual production verification in enterprises, the low pressure casting coating has good surface strength ? interface bonding strength ? stripping performance and long service life. And the surface of aluminum alloy casting is bright and clean.