The easy failures and their causes in the electroplating process of aluminum wheels
1 Poor binding
Poor bonding is mainly manifested as blistering and peeling. Blistering refers to the phenomenon of bulging in a local area between the plating layer and the plating layer. Small bubbles are generally difficult to penetrate with a knife, and large bubbles are similar to peeling after being penetrated, and they also show peeling characteristics.
Peeling refers to the phenomenon that the entire area between the plating layer and the plating layer can be separated and torn off. It is possible between zinc-immersed layer and aluminum alloy, between pre-nickel and zinc-immersed layer, between acid copper and pre-nickel layer, between semi-gloss nickel and acid copper, and between back plating wheel hub and pre-nickel plating. Peeling occurs. The causes of different types are different, and the solutions adopted are different.
The reasons for peeling or blistering between the zinc-deposited layer and aluminum are:
(1) Insufficient components or impurities in the descaling solution; (2) Insufficient concentration of zinc precipitation solution; (3) Low concentration of dezincification; (4) Poor washing before and after zinc precipitation; (5) The content of aluminum impurities in the zinc sink solution is too high. High; (6) The pH of the pre-nickel plating solution is too low; (7) The temperature of zinc precipitation is too high or the alkalinity is high.
The reasons for peeling or blistering between the pre-plated nickel and zinc-immersed layer are:
(1) The pre-nickel-plated live tank device fails; (2) There are many zinc and organic impurities in the pre-nickel solution; (3) The hanger is narrow, the hanger is too dense, and the two sides are shielded.
The reasons for peeling or blistering between the acid copper and the pre-plated nickel layer are:
(1) The lower tank device of the acid copper charging is malfunctioning; (2) The concentration of the activated acid is insufficient or the pre-nickel solution is contaminated by copper impurities; (3) The pre-nickel is contaminated by organic substances containing S (such as impurity removal water, etc.); (4) The workpiece is disconnected in the tank for too long or poor conductivity; (5) The workpiece is electroplated after dropping the cylinder.
The reasons for peeling or blistering between semi-gloss nickel and acid copper are:
(1) The pretreatment is not clean for wax removal or oil removal; (2) The activated acid concentration is insufficient or the use time is too long; (3) The workpiece is poorly conductive in the tank.
The reasons for peeling or blistering between the replated wheel hub and the pre-plated nickel are:
(1) The chrome plating layer has not been completely removed; (2) The storage time of the return wheel hub is too long; (3) The pre-treatment and dewaxing or degreasing is not clean; (4) The surface oxide film is not completely removed; (5) Next The initial current after pre-plating the nickel bath is too large, etc.
2 Pinholes and pits
Pinholes are mostly caused by gas (usually hydrogen) staying on the surface of the plated part. Pinholes are pits, but pinholes are different from pits. They are like shooting stars, often with upward "tails"; while pits are just tiny pits on the coating, the position is sunken, generally not upward The "tail".
Usually, pitting is easy to form in the process of pre-plating nickel, semi-gloss nickel, bright nickel and copper plating.
There are many reasons for the formation of pitting, generally: (1) matrix defect; (2) poor pretreatment; (3) filter pump suction air; (4) poor air stirring; (5) bath temperature is too low and component content Insufficient; (6) Insufficient wetting agent in the plating solution makes the surface tension too large; (7) There are oil stains or too many organic impurities in the plating solution; (8) The surface of the rag for scrubbing the wheel hub is decolorized; (9) The proportion of brightener is out of balance Wait.
Roughness means that there are many small particles on the coating, that is, raised points, which are usually called burrs. The main reasons for the formation are:
(1) Poor pretreatment; (2) The surface of the front wheel hub is rough; (3) The titanium tube of the nickel plating tank has metal powder falling off or bursting; (4) The air used for stirring is polluted by oil, dust, etc.; (5) Anode The bag is broken, and the plating solution is contaminated by anode sludge; (6) There are suspended fine particles (activated carbon, workshop dust, etc.) in the plating solution; (7) When the materials are added, they are not fully dissolved or the raw materials have solid insolubles; (8) The quality of the anode is poor; (9) the process of adding the anode is not sufficiently electrolytic and filtering; (10) the cleaning water is dirty or contains bacteria; (11) the calcium content of the nickel plating solution is >200 mg/L; (12) the metal impurity of the nickel plating solution is iron The hydroxide formed by ions at high pH precipitates in the coating; (13) the hanger or bead is damaged, and the plated metal falls into the tank; (14) the auxiliary anode is bipolar to form a coating and dissolves; (15) the coating is burned The coke forms a sponge-like coating; (16) There is crystallization in the air pump; (17) There is insufficient electrolysis after starting work.
4 White and not bright
Whitening and not bright is easy to form in the low current density area, which is related to the solution itself and the auxiliary anode. The main reasons for its formation are:
(1) Acid copper A additives are not enough; (2) The chloride ion content is too high or too low; (3) The anode area is insufficient; (4) Poor conductivity; (5) The sulfuric acid content is too high; (6) The auxiliary anode does not have electricity Or the current is not large enough; (7) the brightener for nickel plating is too much and the softener is insufficient; (8) the ripple rate of the chrome-plated rectifier is greater than 5%; (9) chloride ion pollution (>50 mg/L); (10) plating After the nickel is left for too long, the nickel layer will be passivated; (11) the purity of sodium carbonate used in the alkaline water used to soak the nickel parts is low; (12) the chromium pre-activation tank is poorly controlled or used too long.
Scorching mainly occurs in the high current density area, which refers to the phenomenon of loosening and blackening of the coating. The main reasons for its formation are: (1) the temperature of the acid copper plating solution is lower than 20 °C; (2) the copper content is too low; (3) the chloride ion content is too low; (4) the brightener A is excessive; (5) lacks Brightener B; (6) Insufficient stirring intensity; (7) Excessive current may cause scorching; (8) The pH in the nickel plating bath is too high; (9) The main salt of the plating bath is too low; (10) The temperature of the bath Too low; (11) a serious excess of wetting agent.
6 Dew yellow
Dew yellow is mainly caused by the poor positioning of the plating solution or the improper installation of the auxiliary anode during chrome plating. Improper chromic acid/sulfuric acid ratio, too much or too little trivalent chromium, too far the auxiliary anode installation position or too small current will cause yellowing. The exposed yellow workpiece should be chrome-plated immediately after reworking.
In the production process, uneven scars are easily formed on the surface or side of the aluminum alloy wheel hub due to excessive local polishing or repairing defects. Especially after the low position is polished to dumb nickel, the nickel wire is applied. Because the thermal expansion coefficients of aluminum, nickel, and copper are different, the aluminum layer is greatly affected by heat during polishing, and the surface of the wheel hub is more likely to form sunken scars after the nickel wire is hung under the wire. If there are multiple scars on the same wheel hub, re-copper should be performed. Only one or two places can be brush-plated and then nickel wire is applied.
Watermark refers to the formation of an irregular flowing water-like white film in the high current density area after bright nickel plating (it can be removed by slight polishing), and it is easier to form the nickel back of the nickel blank. It is generally caused by the oxidation of nickel billets in the air.
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