Aluminum processing pretreatment process details need to pay attention
Aluminum materials are extremely unstable in air, an oxide film is difficult to recognize with the naked eye easily formed. Due to the different pieces of aluminum processing methods, such as cast molding, or by a direct cut from the roll plate, or mechanical precision machining molding, or after molding and then heat treated in different processes or welding, the surface will be presented different states, different degrees of dirt or traces, for the pretreatment step, you must select the process for pre-treatment in accordance with the actual situation of the workpiece surface.
(1) Narrow workpiece pretreatment process needs attention: precision machining parts, although natural oxide film surface before beginning production, easier to clear, but the greasy weight, especially in and around the inner aperture (due to the machining process lubrication needs added), these products must be the work of organic solvent cleaning, if the direct use of alkaline cleaning not only re-greasy difficult Ex, and finely machined surface can not afford a long period of strong base of corrosion, the result will affect the workpiece surface roughness and tolerances of mating, may eventually become waste.
(2) casting molding member pretreatment process issues that need attention. Not all pieces of cast molding surfaces are machined, machined surfaces without leaving thick oxide layer formed during casting, Some also have sand, this time should be used to machining or sand blasting method to remove the original site of the oxide film, or by caustic after processing, the only way to both than the original oxide layer net unprocessed parts and avoid changing the machining tolerances of the parts. (3) problems after heat treatment or welding process workpiece pretreatment step Note: Before according to process requirements, the workpiece into the heat treatment or welding process required by organic solvent cleaning, in addition to the net surface oil, but in general this is not possible that it is the surface layer of oil formed sintered char, char layer which is difficult in addition to the net in an organic solvent, if soaked in lye can cause localized corrosion, pitting or cause uneven, seriously affect the product quality. I concentrated nitric acid immersion approach to this layer of soft foam char, char to be a little soft and then washed in lye that can completely addition to the net.
