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Aluminum extrusion production and processing technology

1. Optimal control of chemical composition

6063-t5 building aluminum profiles must have certain mechanical properties.Under the same other conditions, the tensile strength and yield strength increased with the increase of the content.The strengthening phase of 6063 sets of gold is mainly Mg2Si phase. How much quantity of Mg, Si and Mg2Si should be taken?Mg2Si phase is composed of two magnesium atoms and one silicon atom. The relative atomic mass of magnesium is 24.3 l and the relative atomic mass of silicon is 28.09. Therefore, the mass ratio of magnesium and silicon in Mg2Si compounds is 1.73:1.

Therefore, according to the above analysis results, if the ratio of magnesium-silicon content is greater than 1.73, magnesium in the alloy will not only form Mg2Si phase, but also excess magnesium; otherwise, if the ratio is less than 1.73, it indicates that silicon will form Mg2Si phase and still have residual silicon.

Excess magnesium is harmful to the mechanical properties of alloys.Magnesium is generally controlled at about 0.5%, Mg2Si total control at 0.79%.When there is a surplus of 0.01% silicon, the mechanical properties b of the alloy are about 218Mpa, which has greatly exceeded the national standard performance, and the surplus silicon is increased from 0.01% to 0.13%, b can be increased to 250Mpa, which is 14.6%.To form a certain amount of Mg2Si, the silicon loss caused by impurities such as Fe and Mn must be considered first, that is, a certain amount of excess silicon must be guaranteed.In order for the magnesium in alloy 6063 to fully match the silicon, a conscious effort must be made to make the Mg: Si < 1.73 during the actual batching.The surplus of magnesium not only weakens the strengthening effect, but also increases the product cost.

Therefore, the composition of 6063 alloy is generally controlled as: Mg: 0.45%-0.65%;Si: 0.35%-0.50%;Mg: Si= 1.25-1.30;Impurity Fe < 0.10%-0.25%;Mn < 0.10%.

2. Optimize the annealing process of ingot homogenization

In the production of civil extruded profiles, the high temperature uniform annealing specification of 6063 alloy is 560±20℃, the insulation is 4-6h, the cooling method is forced air cooling or water cooling.

The homogenization of the alloy can improve the extrusion speed and reduce the extrusion pressure by about 6%-10% compared with ingot without homogenization.The cooling rate after homogenization has an important effect on the precipitation behavior of the tissue.For the ingot with rapid cooling after soaking, Mg2Si can be almost completely solidly dissolved in the matrix, and the surplus Si will also be solid solution or dispersion of fine particles.Such ingot can be rapidly extruded at lower temperature and obtain excellent mechanical properties and surface brightness.

In the production of aluminum extrusion, replacing resistance heating furnace with oil or gas heating furnace can achieve obvious energy-saving effect.Reasonable selection of furnace type, burner and air circulation mode can make the furnace obtain uniform and stable heating performance, and achieve the purpose of stabilizing the process and improving the product quality.

After several years of operation and continuous improvement, the combustion ingot reheating furnace with combustion efficiency higher than 40% has been introduced on the market.Ingot furnace charging after heating up quickly to above 570 ℃, and after a period of time of heat preservation, cooling the discharge area close to extrusion temperature extrusion, billets in the heating furnace has experienced the homogenization process, a process called half homogeneous treatment, basically meet the demands of 6063 alloy hot extrusion process, and thus it saves a single homogeneous chemical sequence, can greatly save equipment investment and energy consumption, is a process to be promoted.

3. Optimize extrusion and heat treatment process

3.1 heating of ingot

For extrusion production, extrusion temperature is the most fundamental and critical factor.Extrusion temperature has a great influence on product quality, production efficiency, die life and energy consumption.

The most important problem of extrusion is the control of metal temperature. From the heating of ingot to the quenching of extrusion profile, it is necessary to ensure that the dissolvable phase structure does not separate from the solution or appear the dispersion of small particles.

The heating temperature of 6063 alloy ingot is generally set within the temperature range of Mg2Si precipitation, and the heating time has an important influence on the precipitation of Mg2Si.Generally speaking, the heating temperature of 6063 alloy ingot can be set as:

Inhomogeneous ingot: 460-520℃;Homogenized ingot: 430-480℃.

The extrusion temperature is adjusted according to different products and unit pressure during operation.The temperature of the ingot in the deformation zone changes during the extrusion process. With the completion of the extrusion process, the temperature of the deformation zone gradually increases and the extrusion speed increases.Therefore, in order to prevent the emergence of extrusion cracks, the extrusion speed should be gradually reduced with the progress of the extrusion process and the increase of the deformation zone temperature.

3.2 extrusion speed

The extrusion speed must be carefully controlled during the extrusion process.Extrusion speed has important influence on thermal effect of deformation, deformation uniformity, recrystallization and solid solution process, mechanical properties and surface quality of products.

If the extrusion speed is too fast, the surface of the product will appear pitting, crack and so on.At the same time, too fast extrusion speed increases the inhomogeneity of metal deformation.The outflow rate during extrusion depends on the type of alloy and the geometry, size and surface condition of the profiles.

The extrusion speed of 6063 alloy profile (the outflow speed of metal) can be selected as 20-100 m/min.

With the progress of modern technology, the extrusion speed can be controlled by program or simulated program. Meanwhile, new technologies such as isothermal extrusion process and CADEX have been developed.By automatically adjusting the extrusion speed to keep the temperature of the deformation zone in a constant range, the purpose of rapid extrusion without crack can be achieved.

In order to improve production efficiency, many measures can be taken in the process.When using induction heating, there is a temperature gradient of 40-60℃(gradient heating) along the direction of the length of the ingot.There is also a water cooling die extrusion, that is, in the back end of the mold water forced cooling, the test proved that the extrusion speed can be increased by 30%-50%.

In recent years, nitrogen or liquid nitrogen has been used to cool the die (extrusion die) abroad to increase the extrusion speed, improve the die life and improve the profile surface quality.Nitrogen to the extrusion die exit in the extrusion process, can cause the cooling products rapid contraction, cooling extrusion die and metal deformation area, make the deformation heat is taken away, the mold exit is controlled by the atmosphere of nitrogen at the same time, reduced the aluminum oxide, reducing the alumina adhesion and accumulation, so the nitrogen cooling to improve the surface quality of products, can greatly improve the extrusion speed.CADEX is a newly developed extrusion process, which forms a closed loop system with extrusion temperature, extrusion speed and extrusion pressure during the extrusion process to maximize extrusion speed and production efficiency while ensuring the best performance.

3.3 quenching on machine

The purpose of the 6063-t5 quenching is to preserve the Mg2Si solid dissolved in the matrix metal at high temperature after the mold hole is cooled to room temperature rapidly.The cooling rate is often proportional to the content of the strengthening phase.The minimum hardening rate of 6063 alloy is 38℃/ min, so it is suitable for air quenching.The cooling intensity can be changed by changing the fan and fan revolution, so that the temperature of the product before tension straightening can be reduced to below 60℃.

3.4 tension straightening

After the profile out of the die hole, the general traction with a tractor.When the tractor is working, it moves the extruded products synchronously with the outflow speed of the products with a certain traction tension.The purpose of using the tractor is to reduce the length of multi-wire extrusion and wipe, but also to prevent the profile out of the mold hole after twisting, bending, tension straightening to bring trouble.

Tension straightening can not only eliminate the longitudinal shape of the product, but also reduce its residual stress, improve its strength characteristics and maintain its good surface.

3.5 artificial aging

Aging treatment requires uniform temperature, temperature difference not exceeding ±3-5℃.The artificial aging temperature of 6063 alloy is generally 200℃.The aging insulation time is 1-2 hours.In order to improve mechanical properties, aging of 180-190℃ for 3-4 hours is also used, but the production efficiency will be reduced.