High corrosion resistance aluminum alloy brazing sheet and its vacuum heat treatment process

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The automobile heat exchanger is located at the front end of the automobile, and is subject to pollution from rainwater, salt volatilized from the road, exhaust gas, sand, dust and mud from the automobile, as well as repeated hot and cold cycles and periodic vibrations. Therefore, the composite aluminum foil for automobile heat exchanger requires high corrosion resistance, so as to ensure the service life of automobile heat exchanger. Field use as well as laboratory corrosion test results show that vacuum brazed aluminum foil becomes susceptible to corrosion after vacuum brazing. After brazing, there will be soluble residues including chlorides, bromides and oxides, which are prone to electrochemical corrosion along the interface, that is, between the Al matrix (anodic) and the coarse Si particles (cathodic). corrosion. Once the skin is penetrated, corrosion will continue deep into the core, extending through the thickness, eventually leading to puncture failure of the composite sheet.

A high-corrosion-resistant aluminum alloy brazing sheet and a vacuum heat treatment process thereof, comprising the following steps: preheating and rolling an ingot of an aluminum alloy skin material obtained by smelting, then welding with an ingot of an aluminum alloy core material obtained by smelting, and then welding The aluminum alloy ingot is subjected to hot rolling and preheating, and then hot rolling and cold rough rolling are performed to obtain three-layer aluminum alloy foil, and then the aluminum alloy foil is subjected to intermediate annealing treatment, and finally taken out for finishing rolling, finished annealing, Pull straightening and shearing to obtain finished products.

This process can significantly improve the production efficiency and improve the microstructure and properties. The prepared aluminum alloy composites have excellent corrosion resistance on the basis of maintaining good mechanical properties and brazing properties. An obvious Brownian band is formed in the transition region, which effectively prevents the corrosion from developing in depth.

Through the optimized heat treatment process of the clad aluminum material, the obtained clad aluminum material forms an obvious Brown band during the brazing process, which can effectively inhibit the expansion of corrosion along the depth direction, and improve the corrosion resistance of the composite brazed aluminum plate/foil. It is suitable for Manufacture and use of automotive heat exchangers.

Vacuum annealing with a lower temperature hot rolling preheating process instead of homogenization can keep the alloy with a high Mn solid solubility during processing. The effect of high Mn solid solution elements and the diffusion of Si elements from the skin material can form an obvious precipitation concentration area (that is, Brownian band) in the transition area. The Brown belt can effectively prevent the inward expansion of the intergranular corrosion of the skin material, so it can significantly improve the corrosion resistance of the composite aluminum material. The perforation time of the SWAAT salt spray test is more than 28 days.

The intermediate annealing process in cold rolling can reduce the precipitation size of the core material of the composite brazed aluminum material, which can be used as the second phase of the nucleation core, and precipitate fine and dispersed second phase particles. The fine and dispersed second-phase particles can pin the dislocation and the movement of grain boundaries, delay the recrystallization, and finally form a coarse recrystallization structure, which reduces the way of further expansion of corrosion.

By optimizing the vacuum heat treatment process of clad aluminum, and replacing the long-term homogenization annealing process with the hot rolling preheating process, the method is simple and easy to implement, and the industrial production efficiency is significantly improved.

The heat treatment process of the described high corrosion-resistant aluminum alloy brazing sheet, comprises the following steps:

1) The core material will be prepared according to 3 series aluminum alloy grades (3 series aluminum alloy), such as 3003 or 3003+Cu grades, and prepared according to 4 series aluminum alloy grades (4 series aluminum alloys), such as 4045 or 4343 grades As the raw material of the leather, the core material and the raw material of the leather are respectively added into the melting furnace, and after melting, refining and slag removal at a temperature of 740-760 °C, the leather is obtained by pouring at a temperature of 690-710 °C. Alloy ingots and core alloy ingots;

2) After the skin material alloy ingot is preheated and rolled, welding is carried out in the order of skin material, core material and skin material to obtain a three-layer aluminum alloy ingot;

3) Under the condition of 400-550℃, the welded aluminum alloy ingot is preheated by hot rolling for 8-16h;

4) The preheated aluminum alloy ingot is hot-rolled at 450-470°C, and rolled into a hot-rolled billet with a thickness of 5.8-7.0mm;

5) cold rough rolling the hot-rolled billet to 1.4-2.2 mm on a cold rolling mill to obtain a three-layer aluminum alloy foil;

6) Then, the aluminum alloy foil is subjected to an intermediate annealing treatment in the temperature range of 300 to 450 ° C for 9-12 hours, and then cooled to normal temperature after being taken out;

7) Finish rolling the above-mentioned foil material on a cold rolling mill to an aluminum alloy composite foil with a finished product thickness of 0.20-0.48 mm;

8) When recrystallization annealing is required, the aluminum composite foil is subjected to finished annealing at 380-420° C. for 9-15 hours, and then pulled and straightened after being released from the furnace.

Equipment selection: The RHVB series vacuum heat treatment furnace produced by SIMUWU is a high-quality product for the vacuum heat treatment process of tooling and molds. Good temperature control accuracy and temperature control uniformity ensure the effective progress of the vacuum heat treatment process. SIMUWU specializes in the manufacture of vacuum furnaces, has more than ten years of relevant experience, and has a good reputation in the field of vacuum furnace manufacturing. The product line includes vacuum air quenching furnace, vacuum oil quenching furnace, vacuum annealing furnace, etc., which are widely sold in developed and developing countries.