Defects and solutions of the hottest aluminum allo

Defects and solutions of aluminum alloy bearing plating

aluminum alloy bearing plating is prone to defects of poor coating adhesion. The author discusses the typical faults and solutions of poor coating adhesion encountered in the electroplating of aluminum alloy bearing shells with his peers

1 fault case

1.1 poor pretreatment

1.1.1 fault phenomenon

(1) blistering on the surface of the coating. After the bonding force test, the blistering part of the coating peels off, exposing the aluminum alloy matrix

(2) the surface of the coating is smooth, but after the bonding force test, the coating is partially peeled off, exposing the aluminum alloy matrix

1.1.2 causes and solutions

generally, there are defects of poor adhesion of the coating, and the causes are all in the pretreatment. When the concentration of alkali washing and acid washing solution is not within the process range, or the temperature of degreasing solution is lower than the process range, or the concentration of hydrogen peroxide in acid washing solution is insufficient, poor adhesion of coating will be caused. The solution should be analyzed regularly and added in time to ensure that the composition of the solution is within the process scope

1.2 nickel plating is not timely after zinc immersion

1.2.1 fault phenomenon

after zinc immersion, when the assembly line is not positioned on time, the nickel anode presses against the fixture, so that the workpiece cannot be smoothly in place and nickel plating can be carried out in time, resulting in a large area of pitting on the lead tin coating. The coating is completely peeled off after the bonding force test

1.2.2 causes and solutions

(1) because the surface of aluminum alloy is easy to oxidize, the nickel layer is not easy to be plated, so before nickel plating, zinc dipping should be used as the bonding layer, and nickel plating should be carried out within 1min after zinc dipping, otherwise, the zinc dipping layer will be removed, resulting in a large area of pitting on the lead tin layer, affecting the bonding force of the coating

(2) the zinc dipping solution is too thick, too thin or the component proportion is improper; Or the process conditions are improper, the zinc dipping layer is uneven, or the crystallization is coarse and too thick; Or not electroplating in time after zinc immersion will cause poor adhesion of nickel plating

the zinc dipping solution should be adjusted or replaced in time, and the operation should be carried out in strict accordance with the process conditions. Nickel plating should be carried out within 1min after zinc dipping

1.3 temperature change

1.3.1 fault phenomenon

from December to February of the next year, the coating is prone to poor adhesion defects. From June to September, the surface of the coating begins to bristle. Small micro bubbles can be seen on the surface of the coating through the microscope, but the coating peeling phenomenon is not found through the bonding force test

1.3.2 causes and solutions

we have found this phenomenon for two consecutive years. Check each process. It is found that when the temperature of zinc dipping solution is lower than 15 ℃ in winter, the zinc dipping layer is uneven, and the temperature in summer exceeds 35 ℃. The zinc dipping layer is easy to be removed. Therefore, we add a temperature control device to the zinc bath to control the temperature of the zinc bath at 15 ~ 25 ℃, which solves this problem

1.4 poor activation before lead tin alloy plating

1.4.1 fault phenomenon after electroplating, local coating peeled off, but the nickel layer bonded well with the substrate

1.4.2 causes and solutions

plating tensile test is one of the most widely used methods to study the mechanical strength of materials. 1. Generally, before clamping the two ends of the material sample on two fixtures with a certain distance, lead tin alloy must be activated to make the nickel layer and lead tin layer combine well. However, due to the organic matter contained in the activation solution, the adhesion of the coating becomes poor, so it needs to be treated with activated carbon

at the same time, when electroplating lead tin alloy, the components that fell to 8.5 billion euros on September 30 must be charged into the tank, otherwise, there will be poor bonding between lead tin layer and nickel layer

2 other faults

2.1 air flow trace on the coating surface

2.1.1 fault phenomenon

slight air flow trace from bottom to top appears on the coating surface after electroplating, and there is tactility in serious cases

2.1.2 causes and solutions

(1) organic matter pollution in the plating solution requires continuous filtration with activated carbon for 1 ~ 2 shifts

but also frankly face possible challenges: "the utilization of graphene in some scenarios may be realized in a few years. (2) after the machining process before electroplating, there are burrs, rough surfaces and edges left on the two planes of the bearing bush and the mating plane. Therefore, they should be inspected and removed before plating.

(3) If the cleaning is poor, it is necessary to extend the cleaning time or replace the cleaning water or check whether the air mixing of the cleaning tank is normal

2.2 fault caused by the quality of aluminum alloy material of bearing bush

2.2.1 fault phenomenon

there are scattered transverse pinholes on the surface of bearing bush coating after electroplating. Another major disadvantage of potentiometer sensor is easy to wear

2.2.2 causes and solutions

due to the large amount of production, we believe that it is caused by impurities in the nickel plating solution. Therefore, the nickel plating solution is treated according to the conventional method. However, after two shifts of treatment, there are still transverse pinholes on the surface of the coating. Then we will bore the defective bearing bush. When the plating is removed, we will bore it for 20 μ After the aluminum alloy layer of M, it is found that there are small pits on the surface of the aluminum alloy. We re tested the plating of bearing shells with pits, and obvious pits also appeared on the surface of the coating. Finally, we changed the alloy material to solve this problem