ã€China Aluminum Industry Network】 Aluminum polishing is the foundation for the development of a variety of aluminum, multi-color, light-colored harmonic and colorful aluminum. It is the key technology to change the color tone of aluminum materials and improve the exterior decoration effect of aluminum materials. It is also the main route for the upgrading and appreciation of aluminum materials. With the increasing demand for quality and types of aluminum materials in shopping malls, the prospects for the development of polished aluminum materials are becoming wider and wider. Chemical polishing has the characteristics of simple technology, high polishing speed, low aluminum consumption, can be used for messy workpieces, does not need electricity, and has little capital contribution, so it has been used abroad for more than 100 years. Tri-acid polishing can produce mirror light, but during the polishing process, toxic gases such as N0, N0x, and acid mist can occur. It needs to be properly handled, and there is a certain degree of difficulty in bath protection. The brightness of diacid polishing is slightly lower than that of tri-acid polishing, but the appearance of the polished workpiece is smooth and smooth, and the effect of uniform light is also very good, second only to tri-polished. Because there is no poisonous gas attack during the polishing process and the acid mist is lighter, it has more development prospects. The comparison of various polishing methods is shown in Table 5—5-16.
Table 5—5— Comparison of 16 polishing methods
Electrolytic polishing
Chemical polishing
Mechanical polishing
Evenly dissolved by the metal surface
Bright light
Good corrosion resistance and bright light persistence
Suitable for both soft and hard metals
Misshapen objects can also be polished
Aluminum alloy is more difficult, pure aluminum polishing effect
Large area requires large equipment
Can be used on precision parts
Work needs scientific management
Technical clutter
Specular gloss
Bright light
better
Suitable for both soft and hard metals
Misshapen objects can also be polished
Aluminum alloy is more difficult, pure aluminum effect
Large area requires large equipment
Can be used on precision parts
Work is simpler
Technology is simpler
The metal surface of the cutting friction, smooth mirror surface
Inferior
Inferior
Difficult to implement in soft alloys
Shapes of cluttered objects polished hard
Aluminum alloy can also
No such hardship
Not suitable for fine parts
Brief work
Technical brief
First, the principle of chemical polishing
During the chemical polishing process, the metals are ionically transferred to the solution. These ions accumulate on the surface of the metal being polished, causing an increase in the viscosity of the neighboring electrolyte layer. When the metal is exposed to a highly viscous liquid layer, the dissolution rate is higher than that of the metal. The new solution is small and medium, because the specific gravity of the mucus layer increases, so the interface between the metal and the electrolyte will appear convection appearance. The result is that the metal surface is slightly convex and slightly concave than the mucus layer, and the electrolysis is not abbreviated. The liquid spreads slightly to the bulge at a greater speed, so the bulge dissolves more quickly, while the mucus layer protects the dent and is no longer affected by the electrolyte, ie, the dissolution rate is small, and then reaches the flat metal appearance. The polishing intention.
Second, chemical polishing technology
Chemical polishing technology has a history of nearly one hundred years, many formulations, and now used in production are more:
1 Sulfuric Acid + Phosphoric Acid + Nitric Acid System: Triacid Polishing
2 sulfuric acid + phosphoric acid system: two acid polishing
The ratio of sulfuric acid to phosphoric acid is roughly 1:4, and the nitric acid content is about 5%. Together, copper nitrate, copper sulphate, urea, ammonium sulfate, macromolecule organics such as polyethylene glycol, etc. are also used as additives to suppress yellow smoke and improve the brightness of polishing, but overall, tri-acid bright light is better but yellow smoke can not be based on Elimination, when the temperature is higher than 85 °C transfer time is short, otherwise easy to attack "flow marks", while the transfer time is short, bring out more bath, resulting in high cost. The acid polishing effect is determined by the rational use of the polishing additive.
1) Effect of components in chemical polishing bath
(1) Phosphoric acid: The chemical polishing solution has a high content of phosphoric acid. Phosphoric acid is a medium-strong acid and has a relatively high viscosity. From the above-mentioned chemical polishing mechanism, it can be seen that in order to dissolve and flatten the microscopic projections, the depressions are dissolved as much as possible. It is necessary to have a layer of mucous membranes. The aluminum phosphate produced by the action of phosphoric acid and aluminum is a highly viscous mucous layer.
A1+7H3P04+5HN03=7A1P04+2N2+N02+13H20
Aluminum phosphate from the appearance of the solution to some of the slow dispersion speed, in the metal surface of the dimple, the mucosal layer is thick, slow dissolution, in the micro convex, the dissolution is fast, so that the convex part is dissolved flattened, so acidic chemical polishing solution It is necessary to have a relatively high phosphoric acid, and when the phosphoric acid is insufficient, the polishing effect becomes poor.
(2) Sulfuric acid: Its role is to accelerate the polishing speed, improve the leveling effect, too low (?8%) polishing speed, too high and low polishing quality, the chemical reaction of sulfuric acid in the chemical polishing process is as follows:
2A1+3H2S04=Al2(S04)3+3H2↑
A1203+3H2S04=Al2(S04)3+3H20
(3) Nitric acid: strong oxidizing acid, which can make aluminum surface to form aluminum oxide film, and dissolve aluminum oxide film together to form aluminum nitrate in time, so it plays an important role in polishing quality, too low (<2%) polishing function. Falling, too high (>12%) to attack point corrosion. 3% to 8% are better, and the chemical reaction of nitric acid during polishing is as follows:
2A1+6HN03=A1203+6N02↑+3H20
4A1+4HN03=2A203+4NO↑+2H20
A1203+6HN03=2Al(4N03)3+3H20
(4) The role of heavy metal salts: Participation of heavy metals such as Cu2+ in acidic chemical polishing solutions can improve flatness and reflectivity. The primary copper ion is separated at the defect site of natural oxidation and the metal aluminum matrix undergoes a permutation and then forms a copper atomic layer on the entire surface of the aluminum.
3Cu2++2A1→2A13++3Cu↓
The onset of the above reverberation caused aluminum to have a thin layer of copper. The dissolution of aluminum was difficult. The oxide film could only be dissolved and regenerated repeatedly in some appearances. The copper and the matrix had a seizure potential difference, which could promote the dissolution and flattening of the convex portion, and then improved the polishing effect. .
(5) Smokeless Chemical Polishing Additives: Replace nitric acid to eliminate yellow smoke, adjust viscosity, improve polishing quality, reduce corrosion rate, extend transfer time, and reduce production costs.
Various chemical polishing methods and technical conditions are shown in Table 5—5—17.
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