Abstract: due to the rough etching surface, it becomes a plow skin state. It not only reduces the gloss, but also dissolves excessively, and even affects the dimensional accuracy.

1. Hard Chemical Blackening over etching

Production process: etching

Cause process: etching

Definition: rough surface due to excessive etching.

Phenomenon: due to the rough etching surface, it becomes the plow skin state. It not only reduces the gloss, but also dissolves excessively, and even affects the dimensional accuracy.

Cause: due to improper tank liquid conditions (concentration, temperature), treatment time, reprocessing times, etc., it becomes over etching. The use of additives is also affected. In addition, due to the different alloy composition, extrusion, rolling and other conditions of the treated materials, the results are also different. Countermeasures:

(1) Select appropriate bath conditions (sodium hydroxide concentration, dissolved aluminum amount and temperature);

(2) Select appropriate processing time;

(3) Reduce the number of reprocessing.

2. Hard chemical black dyeing and poor degreasing

Production process: degreasing

Process: degreasing

Definition: uneven etching due to incomplete degreasing

Phenomenon: due to uneven etching, it becomes uneven and presents different luster. After coloring, it becomes a stain.

reason:

(1) The grease attached to the material before surface treatment shall be subject to etching treatment before being removed from the degreasing place;

(2) Degreasing conditions deviate from the control range.

Countermeasures:

(1) Confirm the cutting oil and rust inhibitor used in the extrusion process;

(2) Make the degreasing conditions within the control range.

3. Hard chemical black alkali burn

Production process: etching

Cause process: etching

Definition: uneven gloss caused by excessive reaction of etching solution remaining on the material surface after etching.

Phenomenon: after etching, during the water washing process, the surface of the material will dry, and the etching surface will become uneven and uneven luster.

reason:

(1) Etching solution aging;

(2) The temperature of etching solution is too high;

(3) It takes a long time to wash after etching;

(4) Alkali burns are easy to occur when the temperature is high.

Countermeasures:

(1) Control the etching solution (sodium hydroxide concentration, dissolved aluminum, etc.);

(2) Correct temperature control of etching solution;

(3) Wash immediately after etching.

4. Snowflake corrosion

Production process: water washing before anodizing

Cause process: water washing before anodizing

Definition: pitting corrosion produced in water washing caused by impurities contained in materials.

Phenomenon: spot corrosion occurs in sulfuric acid water washing before anodizing (after sulfuric acid degreasing or neutralization), which is named because its shape is similar to snowflake crystallization. And the surface of the normal part sometimes becomes a glittering plow skin pattern.

Cause: the trace zinc and gallium contained in the material react with the sulfate and aluminum ions dissolved in the washing water before anodizing. The reason why the surface turns into plough skin shape is that different grain boundaries and grain orientation lead to different dissolution, as well as the influence of zinc in the material. The phenomenon similar to the bright pattern occurs in water washing and etching. However, it does not occur in water washing after decontamination with nitric acid.

Countermeasures:

(1) Reduce the content of zinc and gallium in the alloy;

(2) Control the concentration of sulfate and aluminum ions in washing water.

5. Bright pattern

Production process: etching

Cause process: etching

Definition: bright grain dispersed plow skin pattern produced in etching.

Phenomenon: with the increase of dissolved zinc in the etching solution, the dissolution difference caused by grain and grain orientation will appear and become a flashing plow pattern. This phenomenon is clear with etching.

Cause: this phenomenon is caused by the dissolution of zinc in the etching solution and becomes clear with the increase of its concentration. It has been determined that this phenomenon occurs when the concentration of dissolved zinc is 4ppm. This phenomenon is also affected by zinc content, grain size and orientation in the alloy.

Countermeasures:

(1) Remove the zinc dissolved in the etching solution;

(2) Reduce the content of zinc in the alloy;

(3) Prevent grain coarsening.