Overview of Chemical Polishing Aluminium, Electra-chemical Polishing Aluminium and Mechanical Polishing

The general engineering application of wrought aluminium alloy material or building aluminium profile is the process of the semi-finished product. Aluminium extrusion profile manufacturers are generally able to directly put the profiles into anodize production line for anodizing. The obtained anodized film has the good protective properties in many engineering applications, which basically achieves uniform appearance requirements. However, if mechanically polished aluminium work-piece is directly anodized, only the smooth anodize oxide film could be obtained, but fails to get the coating film of high reflective.

Chemical polishing and electro-chemical polishing can give aluminium profile a very shiny surface, but in terms of polishing, chemical polishing (or electro-chemical polishing) are fundamentally different from mechanical polishing: Chemical polishing and electrochemical polishing, as an advanced finishing method, can remove slight mold marks and scratches on the surface of aluminium products; can also remove the friction bands, thermal deformation layer and anodized film layer that may be formed in mechanical polishing. After chemical or electrochemical polishing, the rough surface of aluminium work-piece tends to be smooth and shiny as a mirror, which improves the decorative effect of the aluminium products (such as reflected performance, brightness, etc.). It can also give higher value-added commercial, satisfy the demand for aluminium products with the bright surface. Therefore, chemical polishing or electrochemical polishing treatment is needed pre-processing so as to meet the special surface requirement of smooth, uniform and bright.

Chemical polishing is a kind of chemical corrosion in special conditions, the process is that convex parts of aluminium profile surface are dissolving prior to the concave areas by controlling the selective dissolution, and finally to achieve the goal of surface smooth and bright.Mechanical polishing is the use of physical tools to make aluminium surface plastic deformation by high-speed cutting and grinding, forcing the convex part of the surface to fill in the concave part, thus aluminium profile surface roughness is reduced and smoothed. However, mechanical polishing could cause the damage of metal surface crystallization, even produced plastic deformation layer and tissue change layer due to local heating.

In industrial production, the primary purpose of chemical polishing or electrochemical polishing is to replace the mechanical polishing to obtain the smooth and bright surface; the second is to use chemical polishing or electro-chemical polishing to obtain a very high spectacular reflectance of aluminium and aluminium parts.The process of electrochemical polishing, also known as electropolishing, is similar to chemical polishing which makes the surface smooth and bright by controlling the selective dissolution. Aluminium profile is immersed in a prepared electrolytic solution as an anode, and corrosion resistant material with good conductive as the cathode, according to the principle of electrochemical tip discharge.

This article was written by Walter Liu on https://www.linkedin.com/pulse/overview-chemical-polishing-aluminium-mechanical-walter-liu/
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