CN102286766A - Aluminum alloy hard anode oxidation film and process method thereof - Google Patents

Abstract

The invention relates to an aluminum alloy hard anodized film and a process method thereof. After degreasing and degreasing, the surface of the aluminum alloy workpiece is shot peened with clean stainless steel shot, and then hard anodized in an electrolyte with low sulfuric acid concentration, and hard anodized with low current density and then high current density The hard oxide film is obtained after treatment, the thickness of the oxide film is 340-374 μm, and the hardness is high, the film layer is dense, and it is beneficial to environmental protection and cost reduction.

Description

Aluminum Alloy Hard Anodic Oxidation Film and Its Process Method

technical field

The invention relates to aluminum alloy surface treatment, in particular to the field of hard anodic oxidation treatment with sulfuric acid electrolyte.

Background technique

Aluminum alloy hard anodic oxide film has excellent properties such as high hardness, corrosion resistance, insulation, light function, etc. It is widely used in the fields of automobile, machinery, electronics and aerospace, such as engine aluminum piston, scroll compressor After hard oxidation of parts such as discs and aluminum cylinders, the wear resistance and corrosion resistance can be improved. The micropores in the oxide film can be used to prepare composite membranes, filter membranes, and functional membranes. They can also be used as catalyst carriers and templates to synthesize nanomaterials, etc. .

Common hard anodizing uses a high-concentration sulfuric acid electrolyte, such as an electrolyte with a sulfuric acid content of 150-300g/L. It is generally believed that the oxide film grows at the metal/oxide film/electrolyte interface through the transport of Al ³⁺ and O ^2- in opposite directions, and the formed porous oxide film is separated from the aluminum substrate by a very thin barrier layer (about 1 μm) , and is composed of hexagonal unit cells arranged in an array, and there is a thin and long hole in the unit cell leading to the outer surface. However, in the actual anodizing process, the structure of the oxide film varies greatly due to the type, concentration and temperature of the electrolyte, the composition of the aluminum alloy and the process parameters. In order to obtain high-quality oxide films and production efficiency, different types of electrolytes, additives, current densities, and voltage waveforms (such as DC superimposed pulses or positive and negative pulses) are used in hard oxidation of aluminum alloys, but this is not conducive to environmental protection and energy saving, and the film thickness and performance of the oxide film are still very limited. As we all know, the growth of anodic oxide film is carried out under the competition between the growth rate of the oxide film and the dissolution rate of the electrolyte on the oxide film. Therefore, the lower the acid concentration and temperature of the electrolyte, the smaller the dissolution rate of the oxide film, which is beneficial to the oxidation film. Growth, film thickness and density increase. When the concentration of sulfuric acid is too low (≤10wt% H ₂ SO ₄ ), it is believed that a complete oxide film cannot be obtained, because the concentration of sulfuric acid is low, the conductivity of the electrolyte is poor, the freezing point is high, and the surface of the aluminum alloy has not been specially pretreated.

Contents of the invention

In view of the above existing problems, the object of the present invention is to provide a hard anodic oxidation film of aluminum alloy and its process method, that is, first carry out shot blasting treatment on the surface of aluminum alloy workpiece, and then carry out hard anodic oxidation film in an electrolyte solution with low sulfuric acid concentration. Quality anodic oxidation can prepare a hard oxide film with thick film layer, high hardness and high density, which is beneficial to environmental protection and energy saving, thereby overcoming the deficiencies of the prior art.

The technical solution of the present invention is an aluminum alloy hard anodized film and its process method. The surface of the aluminum alloy workpiece is shot blasted to obtain a high-density, high-surface-energy stress zone, and then low-current density is carried out in a low-sulfuric acid concentration electrolyte. and high current density hard anodizing. This is achieved through the following process methods.

1. The aluminum alloy workpiece after degreasing, degreasing and cleaning is shot blasted on the surface of the aluminum alloy workpiece with clean stainless steel shot in the shot blasting machine for 5-8 minutes. The particle size of the stainless steel shot is 200-70 mesh. Rinse with clean water and dry;

2. Prepare low sulfuric acid concentration electrolyte, sulfuric acid concentration is 30-60g/L, aluminum sulfate is 50-100g/L, tartaric acid is 20-40g/L and ethylene glycol is 100-250g/L, the rest is distilled water or Ionized water;

3. Carry out hard anodic oxidation in a low sulfuric acid concentration electrolyte, the temperature of the electrolyte is -4-3°C, the current adopts a constant direct current or pulse current, and the hard anodic oxidation is carried out according to the following process steps to obtain an oxide film:

(1) Use a low current density of 1-2A/ ^dm2 for hard anodizing for 12-15min;

(2) Carry out hard anodizing with a high current density of 5-7A/dm ² for 80-100min;

(3) Wash with water and dry.

The advantages of the present invention are:

(1) The hard oxide film is thick and has good comprehensive performance. When the thickness of the oxide film is 340-374μm, it still has high hardness and high density.

(2) Conducive to environmental protection, material saving and energy saving. The surface pretreatment of aluminum alloy workpieces is treated with clean stainless steel shot blasting, without alkali washing and pickling, the acid concentration of the electrolyte is extremely low, there are few materials used to prepare the electrolyte, and the temperature of the electrolyte does not rise significantly. There is little corrosion to the oxide film, the film forming speed is fast, and the electrolyte will not be scrapped due to the increase of aluminum ions, and the service life is long.

Detailed ways

The present invention is further described as follows in conjunction with specific embodiment:

Example 1 Hard anodic oxidation of aluminum alloy 5052 plate (200×150×2mm ³ ):

(1) The surface of the aluminum alloy 5052 plate after degreasing, degreasing and cleaning is shot blasted for 5 minutes with clean stainless steel shot in the shot blasting machine. The particle size of the stainless steel shot is 100-120 mesh, and then used Rinse with water and dry.

(2) Preparation of low sulfuric acid concentration electrolyte, obtaining sulfuric acid concentration is 30g/L, aluminum sulfate is 70g/L, tartaric acid is 40g/L and ethylene glycol is 150g/L, all the other are distilled water or deionized water.

(3) Carry out hard anodic oxidation in a low sulfuric acid concentration electrolyte, the temperature of the electrolyte is controlled at -1-1°C, the current adopts a constant direct current, and the hard anodic oxidation is carried out according to the following process steps to obtain an oxide film:

①Using low current density 2A/dm ² for hard anodizing for 13min;

② Hard anodizing with high current density 6A/dm ² for 80min;

③Take it out, wash it with clean water and dry it.

The thickness of the oxide film was detected to be 357 μm, the microhardness was 627 HV, and the density was 3.11 g/mm ³ .

Example 2 Hard anodic oxidation of aluminum alloy 2024 plate (200×150×2mm ³ ):

(1) The aluminum alloy 2024 plate after degreasing, degreasing and cleaning is subjected to shot blasting treatment for 7 minutes in a shot blasting machine with clean stainless steel shot, the particle size of the stainless steel shot is 150-200 mesh, and then Aluminum alloy workpieces are washed with clean water and dried.

(2) preparation low sulfuric acid concentration electrolyte, obtaining sulfuric acid concentration is that sulfuric acid concentration is 50g/L, aluminum sulfate is 80g/L, tartaric acid is 40g/L and ethylene glycol is 200g/L, all the other are distilled water or deionized water.

(3) Perform hard anodic oxidation on the aluminum alloy 2024 plate after shot blasting in the prepared low sulfuric acid concentration electrolyte. The temperature of the electrolyte is kept at -3--1°C, and the current adopts a constant DC current, according to the following The process steps are hard anodic oxidation to obtain an oxide film:

①Use a low current density of 1A/dm ² for hard anodizing for 15 minutes;

② Hard anodizing with high current density 5A/dm ² for 90min;

③Take it out, wash it with clean water and dry it.

The thickness of the oxide film was detected to be 357 μm, the microhardness was 573 HV, and the density was 3.02 g/mm ³ .

Claims (4)

1. aluminium alloy hard anodized film and processing method thereof is characterized in that: to deoil and degreasing after the Al alloy parts surface carry out in low sulfuric acid concentration electrolytic solution, carrying out the hard anodizing processing again after the shot peening with clean stainless shot and obtain hard anodic oxidation coating.The oxide film thickness is 340-374 μ m, and hardness is 540-650HV, and the density of oxide film rete is 2.94-3.11g/mm3;

2. according to the aluminium alloy hard anodized film and the processing method thereof of claim 1, it is characterized in that: described shot peening is to adopt clean stainless shot that shot peening 5-8min is carried out on the Al alloy parts surface in shot-blasting machine, stainless steel pill degree is the 200-70 order, cleans, dries with clear water again after the shot peening.

3. according to the aluminium alloy hard anodized film and the processing method thereof of claim 1, it is characterized in that: the sulfuric acid concentration of described low sulfuric acid concentration electrolytic solution is that 30-60g/L, Tai-Ace S 150 are that 50-100g/L, tartrate are that 20-40g/L and ethylene glycol are 100-250g/L, and all the other are distilled water or deionized water;

4. according to the aluminium alloy hard anodized film and the processing method thereof of claim 1, it is characterized in that: described electrolyte temperature is-4-3 ℃, the hard anodizing electric current adopts constant direct current or pulsed current, carries out hard anodizing by following processing step and obtains oxide film:

(1) uses low current density 1-2A/dm ²Carry out hard anodizing 12-15min;

(2) use high current density 5-7A/dm ²Carry out hard anodizing 80-100min;

(3) clean oven dry with clear water.