[China Aluminum Industry Network] 1 Optimization of chemical composition 6063-T5 architectural aluminum profiles must have certain mechanical properties. When other conditions are the same, the tensile strength and yield strength increase as the content increases. The strengthening phase of 6063 gold is mainly Mg2Si phase. In the end, what is the amount of Mg, Si and Mg2Si? The 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, in the Mg2Si compound, the mass ratio of magnesium to silicon is 1.73: 1.
Therefore, based on the above analysis results, if the magnesium-silicon content ratio is greater than 1.73, the magnesium in the alloy has excess magnesium in addition to the Mg2Si phase, whereas if the ratio is less than 1.73, it indicates that in addition to forming the Mg2Si phase, the silicon also has There is excess silicon.
Excess magnesium is detrimental to the mechanical properties of the alloy. Magnesium is generally controlled at about 0.5%, and the total amount of Mg2Si is controlled at 0.79%. When 0.01% excess silicon, the mechanical properties of the alloy σb is about 218Mpa, has greatly exceeded the national standard performance, and the excess silicon is increased from 0.01% to 0.13%, σb can be increased to 250Mpa, that is, increased by 14.6 %. To form a certain amount of Mg2Si, it is necessary to first consider the loss of silicon due to impurities such as Fe and Mn, that is, to ensure that there is a certain amount of excess silicon. In order to fully match the magnesium in the 6063 alloy with silicon, the actual compounding must be consciously made Mg:Si<1.73. Excess magnesium not only weakens the strengthening effect but also increases the product cost.
Therefore, the composition of the 6063 alloy is generally controlled to: Mg: 0.45% -0.65%; Si: 0.35% -0.50%; Mg: Si = 1.25 - 1.30; impurities in the Fe control <0.10%-0.25%; Mn <0.10%.
2 Optimization of ingot homogenization annealing process In the production of civilian extruded sections, the 6063 alloy high temperature homogenization annealing specification is: 560 ± 20 °C, insulation 4-6h, the cooling method is forced forced air cooling or spray water quenching.
Homogenizing the alloy can increase the extrusion speed, which can reduce the extrusion force by approximately 6% to 10% compared to unhomogenized ingots. After the homogenization treatment, the cooling rate has an important influence on the precipitation behavior of the tissue. For the ingot after rapid cooling, the Mg2Si is almost completely dissolved in the matrix, and excess Si is also dissolved in solid solution or dispersed as fine particles. Such ingots can be extruded rapidly at lower temperatures and achieve excellent mechanical properties and surface brightness.
In the extrusion production of aluminum profiles, replacing the resistance heating furnace with a fuel or gas heating furnace can receive significant energy saving and consumption reduction effects. Reasonable choice of furnace type, burner and air circulation method can make the furnace obtain uniform and stable heating performance, and achieve the purpose of stabilizing the process and improving product quality.
The combustion type ingot heating furnace has been operating and continuously improved over the past several years. Currently, a furnace having a combustion efficiency of more than 40% has been introduced on the market. After the ingot has been loaded into the furnace, it is quickly heated to 570°C or more, and after a certain period of holding time, it is extruded in the discharge zone when it is cooled to near the extrusion temperature, and the ingot undergoes a semi-uniform process in the heating furnace. This process is called Semi-homogeneous treatment is basically in line with the 6063 alloy hot extrusion process requirements, which can save a separate homogenization process, can greatly save equipment investment and energy consumption, is a process worthy of promotion.
3 Optimization of extrusion and heat treatment processes 3.1 Ingot heating For extrusion production, extrusion temperature is a more basic and critical process factor. Extrusion temperature has a great influence on product quality, production efficiency, die life, and energy consumption.
The most important issue in extrusion is the control of the metal temperature. From the beginning of the ingot heating to the quenching of the extruded profile, it is necessary to ensure that the dissolvable phase structure does not precipitate out of the solution or present a dispersal of small particles.
6063 alloy ingot heating temperature is generally set in the Mg2Si precipitation temperature range, the heating time has an important impact on the precipitation of Mg2Si, using rapid heating can greatly reduce the possible precipitation time. In general, the heating temperature of the 6063 alloy ingot can be set to:
Ununiformized ingot: 460-520°C; homogenized ingot: 430-480°C.
The extrusion temperature varies depending on the product and unit pressure during operation. During the extrusion process, the temperature of the ingot in the deformation zone is changed. With the completion of the extrusion process, the temperature in the deformation zone gradually increases, and increases as the extrusion speed increases. Therefore, in order to prevent the occurrence of squeezing cracks, the extrusion speed should gradually decrease as the extrusion process progresses and the temperature in the deformation zone increases.
3.2 Extrusion speed The extrusion speed must be carefully controlled during extrusion. The extrusion speed has an important influence on the thermal effect of deformation, the uniformity of deformation, the process of recrystallization and solution, the mechanical properties of the product and the surface quality of the product.
Extrusion speed is too fast, the product surface will appear pitting, cracking and other trends. At the same time, the extrusion speed increases the non-uniformity of metal deformation. The speed of squeezing depends on the type of alloy and the geometry, size, and surface condition of the profile.
6063 alloy profile extrusion speed (metal outflow speed) can be selected from 20-100 meters / min.
With the advancement of modern technology, the extrusion speed can achieve program control or simulation program control, as well as new technologies such as isothermal extrusion technology and CADEX. By automatically adjusting the extrusion speed to maintain the temperature of the deformation zone within a certain constant range, the purpose of rapid extrusion without cracking can be achieved.
In order to increase production efficiency, many measures can be taken in the process. When induction heating is used, there is a temperature gradient of 40-60°C (gradient heating) along the length of the ingot. When extruding, the high temperature end faces the extrusion die and the low temperature end faces the extrusion pad to balance part of the heat of deformation; Extrusion of the water-cooled die, that is, forced cooling at the back end of the die, tests have shown that the extrusion speed can be increased by 30%-50%.
In recent years, nitrogen or liquid nitrogen has been used to cool molds (extrusion dies) in foreign countries to increase the extrusion speed, improve die life, and improve the surface quality of profiles. In the extrusion process, nitrogen is introduced to the outlet of the extrusion die to rapidly shrink the cooled product, cool the extrusion die and the metal in the deformation zone so that the heat of deformation is taken away, and at the same time, the outlet of the die is exposed to the nitrogen atmosphere. The control reduces the oxidation of aluminum and reduces the bonding and accumulation of alumina. Therefore, the cooling of nitrogen improves the surface quality of the product and can greatly increase the extrusion speed. CADEX is a new extrusion process that has been developed recently. It forms a closed-loop system with the extrusion temperature, extrusion speed, and extrusion force in the extrusion process to greatly increase the extrusion speed and production efficiency. More excellent performance.
3.3 On-machine quenching The 6063-T5 quenching is used to rapidly cool the Mg2Si quenched to room temperature after it is dissolved in the matrix metal at high temperature. The cooling rate is usually proportional to the content of the strengthening phase. The 6063 alloy can be strengthened with a smaller cooling rate of 38°C/min, making it suitable for air-cooled quenching. Changing the fan and fan revolutions can change the cooling intensity so that the temperature of the product before the tension leveling is reduced to below 60°C.
3.4 Tension Straightening profiles After the holes are ejected, they are generally pulled by a tractor. When the traction machine is working, it takes a certain pulling tension on the extruding product and simultaneously moves with the unloading speed of the product. The purpose of using the tractor is to reduce the length of the multi-line extrusion and scratches, but also to prevent the profile out of the hole after the twist, bending, tension tension to bring trouble.
Tension straightening can not only eliminate the longitudinal shape of the product, but also reduce the residual stress, improve the strength properties and maintain its good surface.
3.5 Artificial aging aging requires uniform temperature, temperature difference does not exceed ± 3-5 °C. 6063 alloy artificial aging temperature is generally 200 °C. Aging time is 1-2 hours. In order to improve the mechanical properties, there are 180-190 °C aging 3-4 hours, but at this time the production efficiency will be reduced.
3.6 Optimization and Calculation of Ingot Length The method for calculating the length of the ingot is volume method and mass method. By establishing a mathematical relationship, it is easy to select a better ingot specification and greatly increase the geometric yield of the profile.
(1) Volume method Vo=V1 ten Vn
AoLo=A1·L1 ten A·Ln
Lo/Ko=L1/λ ten Ln
Lo=(L1/λ+Ln)·K
Where: Vo - ingot volume (mm3);
V1 - profile volume (mm3);
Vn - pressure relief volume (mm3);
Ao - ingot area (mm2);
Lo——ingot length (mm);
A1 - profile cross-sectional area (mm2);
L1 - profile length (mm);
A - squeeze cylinder area (mm2);
Ln——pressure length (mm);
K=A/Ao filling factor;
λ = A/A1 extrusion coefficient.
According to the same principle of volume, after being simplified, it can be regarded as formula (1). K and Ln can be regarded as constants. Only λ is required, and Lmax is determined. Lo, which is the length of the ingot, can be conveniently found.
(2) Quality law mo=m1 ten mn
ÏLoLo=L1·ÏL1+mn
Lo=(L1·ÏL1+mn)·PLo
Where: Lo ingot length;
L1 profile extrusion length (m);
ÏL1 profile line density (Kg/m);
Mn excess weight (Kg);
Mo ingot weight (kg)
M1 extrusion profile weight (kg)
ÏLo ingot linear density (Kg/m);
(2) can be changed again, namely: L1 = n · L fixed + L12
Lo=[·L set ten L12)·ÏL1+mn]·ÏLo-1
In the formula: n number of lengths;
L set size length (m);
L12 cut tail cut length (m).
(3) The formula is more intuitive and more convenient to calculate Lo in the actual work ÏL1 is increasing with the continuous change of wall thickness of the profile. In order to facilitate the feeding of the ingots, the length of ingots for large equipment can be set to 30mm, and the small equipment to 20mm to 1st gear. We can formulate the ÏL1, Lo, n, L1 comparison table according to formula (3). General civil building profiles supply length is 6m. This comparison table is very convenient for the use of process technicians and planners.
Formula (3) can be simplified to the following formula:
Lo=KnL1+C
Kn is the coefficient related to n;
C is a model-related constant;
ÏL1 is a function of Lo, which can be programmed into the computer to calculate Lo more accurately.
3.7 Measures to increase the yield of extrusion products Many factors that affect the yield rate of extruded profiles We can calculate geometric wastes. The waste generated in extrusion production is generally divided into geometric waste and technical waste. Geometric waste is the production process. Only waste related to the production process of the product. Pressure residue, cutting head, cut tail, etc. are all geometric waste. In the production process, technical wastes are caused by improper execution of technical operating procedures, resulting in artificial waste (including scraps from trial molds, scraps from casting defects, etc.). Technical waste can be avoided and reduced. Geometric waste is inevitable, but it can be reduced by optimizing the extrusion process and accurately calculating the length of the ingot.
The size of geometric waste in extrusion production can be expressed by the following formula:
N=Nn ten N12
N few waste (%)
Nn scrap (%)
N12 cutting waste (%)
Hn=K/Lo·Ln
N12=K/Lo·L12/λ
N=K/Lo·(Ln+L12/λ)
N=K/Lo·(Ln+L12/λ)
K filling factor;
Lo ingot length (mm);
Ln residual length (mm, varying with barrel diameter);
L12 cut head and tail (mm, change with the product specifications);
λ squeeze coefficient.
From equation (6), it can be clearly seen that the longer the length Lo of the ingot and the larger the coefficient of extrusion, the smaller the geometric waste N, that is, the higher the geometric yield. The ingot length has a greater influence. However, Lo and λ cannot be increased without limit, because they are limited by factors such as extruder capacity, extrusion length, and the like.
4 Summary In summary, the ways to increase the yield of extruded profiles are:
(1) Formulate scientific and reasonable production process (optimized process);
(2) Put forward high technical standards for employees and continuously summarize production experience;
(3) The mold design is advanced and reasonable and the mold management is strengthened to increase the qualification rate of one-time machine operation;
(4) Optimize the chemical composition of 6063 alloy, improve the quality of the ingot and homogenize or semi-uniformize it;
(5) Adopt advanced technologies, such as long-ingot furnace heat shear technology and CADEX and other new technologies.
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