The surface treatment of aluminum alloy die castings is divided into pre-treatment and post-treatment. The pre-treatment is to remove the surface oxide scale and oil stains, increase the post-treatment adhesion and improve the appearance. Shot blasting and sandblasting are the most commonly used pre-treatments for the surface of aluminum alloy die castings, and four types of post-treatments are generally spraying, oxidation, electroplating, and electrophoresis.
Surface pretreatment method
1. Manual processing:
Such as scrapers, wire brushes or grinding wheels. The rust and oxide scale on the surface of the workpiece can be removed by hand, but manual treatment is laborious.
High dynamic intensity, low production efficiency, poor quality and incomplete cleaning.
2. Chemical treatment:
It mainly uses acid-base or alkaline solution to chemically react with oxides and oil stains on the surface of the workpiece, so that it can be dissolved in an acidic or alkaline solution to remove rust, oxide scale and oil stains on the surface of the workpiece.
3. Mechanical treatment method:
Mainly include wire brush roll drawing method, mechanical polishing method, shot peening method.
Depending on the method used, surface post-treatment techniques can be divided into the following categories.
1. Electrochemical method
This method uses electrode reaction to form a coating on the surface of the workpiece.
The main methods are:
2. Chemical methods
This method is no current action, the use of chemical interaction to form a plating layer on the surface of the workpiece.
The main methods are:
(1) Chemical conversion coating treatment
(2) Electroless plating
3. Thermal processing method
In this method, the material is melted or thermally diffused under high temperature conditions to form a coating on the surface of the workpiece.
Its main methods are:
(1) Hot dip plating
(2) Thermal spraying
(3) Hot stamping
(4) Chemical heat treatment
4. Vacuum method
This method is a process in which materials are vaporized or ionized and deposited on the surface of the workpiece in a high vacuum state to form a coating.
Its main method is:
(1) Physical vapor deposition (PVD)
(2) Ion implantation
(3) Chemical Vapor Deposition (CVD)
Spraying is a coating method that is dispersed into uniform and fine droplets by means of pressure or centrifugal force through a spray gun or disc atomizer and applied to the surface of the object to be coated.
It can be divided into:
(1) Air spray
(2) Airless spray
(3) Electrostatic spraying