An optimal control of chemical composition
6063-T5 aluminum construction must have certain mechanical properties. In other conditions, its tensile strength, yield strength increases with increasing concentration. The 6063 alloy main strengthening phase Mg2Si phase, in the end Mg, Si, and the amount of Mg2Si how much should be taken as good? Mg2Si phase is composed of two magnesium atoms with a silicon atoms, the relative atomic mass of magnesium is 24.3l, the relative atomic mass of silicon is 28.09, so Mg2Si compounds, magnesium mass ratio of 1.73:1 silicon.
Thus, according to the above analysis, if the ratio of magnesium and silicon content greater than 1.73, the addition of magnesium alloy to form Mg2Si phase, there is excess magnesium, whereas the ratio is less than 1.73, it indicates that the formation of Mg2Si phase in addition to outside silicon , and the remaining silicon.
Excess of the mechanical properties of magnesium alloys is harmful. Magnesium is generally controlled at about 0.5%, Mg2Si total control at 0.79%. When 0.01% of excess silicon alloy mechanical properties σb about 218Mpa, has greatly exceeded the national standard performance, and the excess silicon from 0.01% to 0.13%, σb can be increased to 250Mpa, namely, to increase 14.6 %. To form a certain amount of Mg2Si, you must first take into account the impurities such as Fe and Mn due to the loss of silicon, that is, to ensure that there is a certain amount of excess silicon. For 6063 the magnesium alloy with the silicon to fully match the actual ingredients must consciously make the Mg: Si <1.73. Excess of magnesium not only weaken the strengthening effect, and also increased the cost of the product.
Therefore, the 6063 general control of alloy composition: Mg: 0.45% -0.65%; Si: 0.35% -0.50%; Mg: Si = 1.25-1.30; Fe impurity control <0.10% -0.25%; Mn <0.10%.
2 Optimization of ingot homogenization annealing
Extrusion in civilian production, the 6063 high-temperature alloy homogenized specification: 560 ± 20 ℃, heat 4-6h, forced air cooling or water to quench released.
Uniform alloy extrusion processing can improve the speed, with no homogenization of the ingot than can squeeze pressure of approximately 6% -10% lower. Cooling rate after homogenization precipitation behavior of the organization has important implications. After the rapid cooling of both the ingot hot, Mg2Si almost all the solid solution in the matrix, the Si excess will precipitate solid solution or dispersion of fine particles present. Such ingots can be extruded at lower temperatures quickly, and get excellent mechanical properties and surface brightness.
In the aluminum extrusion production to replace oil or gas furnace resistance furnace to receive significant energy saving effect. Rational choice of furnace, burners and circulating air oven method allows to obtain uniform and stable heating performance, stable technology to improve product quality.
Combustion ingot furnace to run over the years and continue to improve, the market has launched combustion efficiency higher than 40% of the furnace. Ingot furnace installed quickly heated to above 570 ℃, and after a period of holding time, in the discharge area when cooled to temperatures close to baked extrusion extrusion, ingot furnace through a semi-uniform in the process, this process is called semi-homogeneous process, basically in line with 6063 alloy hot extrusion process requirements, which can be saved separate homogenization process, this will reduce investment in equipment and energy consumption, is a worthy process.
3 Optimization of extrusion and heat treatment processes
3.1 ingot heating
Of extrusion, the extrusion temperature is the most basic and most critical process factors. Extrusion temperature on product quality, productivity, die life, and so have a great impact on energy consumption.
Squeeze the most important issue is the metal temperature control, heated from the beginning to the extrusion ingot quenched phase should ensure that the organization is not soluble in the precipitation from solution or dispersion of small particles present precipitation.
6063 alloy ingot heating temperature is generally set in the Mg2Si precipitation temperature range, the heating time of Mg2Si precipitation has important implications, the use of rapid heating can greatly reduce the possibility of precipitation time. In general, the 6063 alloy ingot heating temperature can be set to:
Not homogenized ingot :460-520 ℃; homogenized ingot :430-480 ℃.
The extrusion temperature during operation depending on the size of products and units of pressure to adjust. In the extrusion process the temperature of the ingot in the deformation zone is changing, with the completion of the extrusion process, the deformation zone temperature gradually increased, and with the extrusion speed increase and increase. Therefore, in order to prevent extrusion crack, with the extrusion process of the deformation zone and the temperature, extrusion speed should be gradually reduced.
Extrusion rate of 3.2
Extrusion process must be carefully controlled extrusion speed. Extrusion rate of thermal effects on deformation, deformation uniformity, recrystallization and solution processes, products, mechanical properties and surface quality of products have an important impact.
Squeeze too fast, the product surface will be pitting, cracks and other tendencies. At the same time squeeze too fast an increase of metal deformation inhomogeneity. Extrusion of the flow rate depending on the alloy type and profile geometry, dimensions and surface conditions.
6063 alloy profile extrusion speed (metal flow rate) can be selected as 20-100 m / min.
Modern technology, extrusion speed can achieve process control or process control simulation, but also the development of isothermal extrusion process and the CADEX and other new technologies. By automatically adjusting the speed of the extrusion deformation zone maintained at a constant temperature range can be achieved by rapid extrusion without cracks purposes.
In order to improve production efficiency, the process can take many measures. When using induction heating, the direction along the ingot length of the existence of temperature gradient 40-60 ℃ (gradient heating), extrusion temperature side toward the extrusion die, extrusion pad toward the low end to balance the part of the deformation heat; there is also water-cooled die extrusion, that back in the mold with water forced cooling, extrusion speed test proven to increase 30% -50%.
In recent years in foreign countries with nitrogen or liquid nitrogen cooled mold (extrusion die) to increase the extrusion rate and improve the die life and improved surface quality profiles. Nitrogen in the extrusion process will lead to the extrusion die exit release, the product can be cooled rapidly shrinking, cooling extrusion die and metal deformation zone, the deformation heat is taken away, while the mold exit was the atmosphere of nitrogen control, reducing the aluminum oxide, aluminum oxide bonding and reduce accumulation, so the nitrogen cooling to improve the surface quality of the products can greatly improve the extrusion speed. CADEX is a recently developed a new extrusion process, extrusion process in which the extrusion temperature, extrusion speed and extrusion pressure to form a closed loop system to maximize production of extrusion speed and efficiency, while ensuring the best performance.
3.3 On-line quenching
6063-T5 is to be quenched at a high temperature solid solution in the matrix metal in the mold hole Mg2Si by rapid cooling to room temperature after being retained. Constant cooling rate and the strengthening phase proportional to the content. 6063 alloy can enhance the cooling rate of the minimum 38 ℃ / min, so suitable for air-cooled quenching. Change the fan and fan speed can change the cooling intensity, so straightening products in tension before the temperature dropped below 60 ℃.
3.4 Tension Straightening
After the mold hole profiles, are generally used tractor traction. Tractor work products in order to squeeze some traction tension while outflow speed synchronization and mobile products. The purpose of using the tractor to reduce the length of multi-line extrusion missing and wiping injury, but also to prevent the mold hole profiles Twisting, bending, tension straightening to cause trouble.
In addition to the tension straightening products can not eliminate the vertical shape of the whole, but also can reduce the residual stress and improve the strength properties and can maintain its good surface.
3.5 artificial aging
Aging required temperature uniformity, temperature does not exceed ± 3-5 ℃. 6063 alloy to artificial aging temperature is 200 ℃. Time holding time of 1-2 hours. In order to improve mechanical properties, but also the use of 180-190 ℃ time 3-4 hours, but this time the production efficiency will be reduced.
3.6 Optimization and calculation of the length of the ingot
Ingot length is calculated with volume method and quality of law. Through the establishment of mathematical relationships, it is easy to select the best ingot size, greatly enhance the profile of the geometric yield.
(1) volume method
Vo = V1 ten Vn
AoLo = A1 · L1 ten A · Ln
Lo / Ko = L1 / λ ten Ln
Lo = (L1 / λ + Ln) · K ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... (1)
Where: Vo - ingot volume (mm3);
V1 - Profile volume (mm3);
Vn - pressure over the volume (mm3);
Ao - ingot area (mm2);
Lo - ingot length (mm);
A1 - profile cross-sectional area (mm2);
L1 - profile length (mm);
A - Extrusion area (mm2);
Ln - pressure over the length (mm);
K = A / Ao filling factor;
λ = A/A1 squeeze factor.
Accordance with the volume constant truth, after the finishing of the simplified formula (1), K and Ln can be considered constant, only requires λ, determine Lmax, can be easily calculated Lo, the ingot length.
(2) Quality Law
mo = m1 ten mn
ρLoLo = L1 · ρL1 + mn
Lo = (L1 · ρL1 + mn) · PLo ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... (2)
Where: Lo ingot length;
L1 profile extrusion length (m);
ρL1 profile linear density (Kg / m);
mn pressure than the weight (Kg);
mo ingot weight (kg)
m1 extrusion profile weight (kg)
ρLo ingot linear density (Kg / m);
(2) what can be changed, that is: L1 = n · L set + L12
Lo = [· L be ten L12) · ρL1 + mn] · ρLo-1
... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... (3)
Where: n Length of count;
Fixed size fixed length L (m);
L12-cut head and tail cut length (m).
(3) more intuitive and convenient to calculate the actual work ρL1 Lo is changing as the profile wall thickness increased. To facilitate the process for the ingot, the ingot length of the large equipment can be set to 30mm for a file, a small device is set to 20mm for a file. We can according to the formula (3) developing ρL1, Lo, n, L1 table. General civil construction supplier profile length 6m. This table technicians and planners of the process is very easy to use.
Equation (3) and can be simplified as the following formula:
Lo = KnL1 + C ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... (4)
Kn is n-related factor;
C is a constant related with the model;
ρL1 is a function of Lo can be programmed into the computer, more accurately calculate the Lo.
3.7 Measures to improve the yield squeeze
Impact extrusion yield many factors we can calculate the geometric waste generated in the extrusion of waste is generally divided into geometric and technological waste waste waste is the production process geometry and product manufacturing processes only the waste. Pressure over, cut head, tail, etc. are the geometric cut waste. Technology waste in the production process, due process procedures not performed correctly, caused by human waste (including waste tryout, casting defects caused by waste, etc.). Technique is to avoid and reduce waste, and geometric waste is inevitable, but can squeeze through the optimization process and accurately calculate the length of other measures to reduce the ingot.
Extrusion in the geometric size of waste can be expressed as:
N = Nn ten N12 ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... (5)
Wait a few N waste (%)
Nn pressure remaining waste (%)
N12 cutting head waste (%)
Hn = K / Lo · Ln
N12 = K / Lo · L12 / λ
N = K / Lo · (Ln + L12 / λ) ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... (6)
N = K / Lo · (Ln + L12 / λ)
K filling factor;
Lo ingot length (mm);
Ln pressure over the length (mm, with the extrusion cylinder diameter change);
L12-cut head and tail (mm, with product specifications and change);
squeezing factor λ.
From (6) Where it is clear that the longer the ingot length Lo, squeezing coefficient is larger, the smaller the geometry waste N that yield higher geometry. Some of which influenced the ingot length. However, Lo and can not increase without limit λ, because they are affected by extrusion capacity, pressure and other factors out the length limit.