ã€China Aluminum Industry Co., Ltd】Axle bush is a key component in the engine. Due to the high engine speed and heavy load, it requires a higher binding force for the coating.
The aluminum alloy bearing aluminum has high chemical activity and the surface is easily oxidized. Even if the surface oxide layer is removed, a new oxide film will be formed in a short time. Therefore, the aluminum alloy bearing bush plating is more difficult than the copper lead alloy bearing.
Plating process flow:
Degreasing→Pickling→Zinc leaching→Nickel plating→Plating Pb-Sn aluminum alloy bearing bushings are prone to defects in coating adhesion. The authors discuss the typical failures and solutions of poor plating adhesion encountered by aluminum alloy bushings and their peers.
Precautions before the failure of the fault phenomenon (1), the surface of the coating blisters, the binding force test, part of the blistering coating peeling, exposing the aluminum alloy substrate.
(2) The surface of the coating is smooth, but after the binding force test, the coating is locally peeled off to expose the aluminum alloy substrate.
Causes and Solutions There are generally defects in poor adhesion of the plating, and the causes are all pre-processing. When the concentration of caustic washing and pickling solution is not within the range of the process, or if the temperature of the degreasing solution is lower than the range of the process, or the concentration of hydrogen peroxide in the pickling solution is insufficient, the adhesion of the plating layer will be poor. The solution should be analyzed periodically and added in a timely manner to ensure that the solution components are within the process.
After the zinc immersion, the problem of nickel plating is not timely. After the immersion zinc, when the assembly line is not positioned correctly, the nickel anode is clamped to the fixture, so that the workpiece can not be successfully placed in time to nickel, resulting in a large area of ​​pewter tin coating. After the bond strength test, the plating was all peeled off.
Causes and Solutions (1) As the surface of the aluminum alloy is easily oxidized, the nickel layer is not easy to be plated. Therefore, before the nickel plating, zinc is first used as a bonding layer, and after the zinc plating, nickel plating is performed within 1 min. Otherwise, the dipping is performed. The zinc layer will recede, resulting in a large area of ​​pewter tinned and affecting the bond strength of the coating.
(2) Immersion zinc solution is too thick, too dilute or improper proportion of components; or improper process conditions, uneven zinc galvanized layer or crystal thick, too thick; or not timely plating after zinc immersion, will cause poor nickel-plating bonding .
The zinc dipping solution shall be adjusted or replaced in time, and the operation shall be strictly performed according to the process conditions. Nickel plating shall be carried out within 1 min after the zinc dipping.
Temperature change failure phenomenon from December to February of the following year, the coating is prone to bond defects. From June to September, the coating surface began to fluff. Microscopic bubbles can be seen on the surface of the coating through the microscope, but no peeling of the coating was found after the binding force test.
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