Solar frame aluminum profile surface quality analysis
[Abstract] With the rapid growth of the economy, the ensuing energy supply will usher in a greater and more serious challenges. Known for energy saving and environmental protection of the photovoltaic industry is becoming more and more intense, the photovoltaic industry involved in the solar energy frame aluminum profile industry has also been rapid development. Solar frame aluminum profiles are mainly used in photovoltaic solar panel frame and play a force support role, the mechanical properties, geometry, surface quality, corrosion resistance have extremely strict requirements of high quality and high standards. This article from the company’s production of solar energy frame aluminum alloy material, extrusion process, die design and other aspects of process analysis, focusing on on-site production practice and theoretical analysis.
I. Purpose and significance of the analysis
Solar frame aluminum profiles as an important accessory for photovoltaic solar energy due to long-term exposure in the field, the natural environment is harsh, manufacturers require its service life of more than 15 years, and in turn, its surface quality requirements are strict, especially the corrosion resistance of the requirements of a higher level. Profiles are fully automated and mechanized when assembled, so the requirements for geometry are particularly strict. At present, customers generally adopt GB/5237-2017, JISH4100, ENI2020.2, JISH8602 and other standards for implementation.
Due to the high surface quality requirements of solar energy frame aluminum alloy profiles, basically most of them are produced by 6005 alloy and 6063 alloy. Our customers require that the frame profiles are processed in accordance with the requirements of GB/T5237-2017 high-precision level; the surface treatment shall be sandblasted silver-white oxidized; and the appearance requirements are subject to strict inspection and control. In order to achieve strict surface quality requirements, reduce the pressure of the subsequent surface treatment process, to ensure that the mechanical properties of aluminum profiles and corrosion resistance; thereby increasing productivity and profile yield; and thus ensure that the enterprise can obtain reliable economic benefits. Therefore, it is extremely important to adopt feasible production process solutions and select ingot aluminum rods with alloy compositions up to standard for profile production and quality requirements. In this paper, only from the solar energy frame aluminum profile alloy composition, extrusion production process, die design and maintenance of three aspects of the analysis overview.
2. Solar frame aluminum alloy composition analysis
1. Determination of chemical composition
The solar energy frame aluminum profile produced by our company is mainly used in the photovoltaic solar panel frame and plays the role of force support, the mechanical properties of which are more stringent than those of general industrial aluminum profiles. In order to meet the high quality requirements of aluminum profiles, the choice of 6063 alloy, 6005 alloy cast bar production. By reviewing relevant information, collecting the company’s aluminum bar alloy composition of the laboratory data, data collation and analysis to obtain the following results:
6063 Alloy
Alloy Materials |
Availability Status |
Wall thickness/mm |
Tensile strength (N/mm²) |
Wechsler hardness HW |
|---|---|---|---|---|
|
T6
|
≤10
|
≤205
|
≤8
|
12-16
|
|
T5
|
≤10
|
≤160
|
≤8
|
11-14
|
|
T4
|
≤10
|
≤115
|
≤6
|
3-7
|
Table 1 - Room temperature longitudinal mechanical properties of 6063 material
According to the mechanical property indexes listed in Table-1, alloy grades 6063-T6, 6063-T5 and 6063-T4 can meet the requirements of material Wechsler hardness ≥14HW (6063-T6).
Table 2-The company 6063 aluminum bar alloy composition internal control standard (mass fraction) %
6063 |
Si |
Mg |
Fe |
Cu |
Mn |
Cr |
Zn |
Ti |
|---|---|---|---|---|---|---|---|---|
|
Internal Control
|
0.38-0.12
|
0.53-0.57
|
<0.20
|
<0.05
|
<0.01
|
<0.05
|
<0.05
|
0.01-0.03
|
|
Results
|
0.379
|
0.564
|
0.151
|
0.037
|
0.034
|
0.014
|
0.0010.0238
|
According to the alloy composition of 6063 aluminum bar listed in Table-2, its alloy composition basically meets the production standards. For 6063 aluminum alloy, reasonable adjustment of the quality ratio of Si and Mg elements helps to improve the comprehensive performance of the material, and the appropriate excess of Si elements is beneficial to grain refinement and improvement of alloy strength. Practice has proved: 6063 alloy to take into account the surface quality, mechanical properties, extrusion performance, the alloy should reduce the content of Fe, reduce the alloy containing Fe phase, and thus improve the surface quality of the profile. In order to make the alloy easy to extrude the same level, reduce the content of Mg, more effective than reducing the content of Si; in order to ensure the mechanical properties of the profile, so that the alloy’s Si excess ≤ 0.25%, the formation of more single-crystal Si, the strength should be greater than the hardness of the reinforced phase.
Mg content in the alloy is too high, extrusion surface pitting, white spots are more, not conducive to extrusion; Si content is too high, the profile surface is easy to appear irregularly dragged, and once the mold design has a little defect, it is easy to produce black line. If the production of bright material, coloring material and electrophoretic painting material, Mg/Si in the range of 1.5-1.7 better, this is because there is less excess Si, profile corrosion resistance is good, easy to get a bright surface.
Due to the high surface quality requirements of solar aluminum profiles, in order to reduce the pressure of the surface treatment process, but also to ensure the mechanical properties of the profiles, when adjusting the alloying elements, it is necessary to appropriately increase the lower limit of the Cu element, the addition of Cu and unsuitable heat treatment can increase the intergranular corrosion susceptibility of aluminum alloys.
Mg content in the alloy is too high, extrusion surface pitting, white spots are more, not conducive to extrusion; Si content is too high, the profile surface is easy to appear irregularly dragged, and once the mold design has a little defect, it is easy to produce black line. If the production of bright material, coloring material and electrophoretic painting material, Mg/Si in the range of 1.5-1.7 better, this is because there is less excess Si, profile corrosion resistance is good, easy to get a bright surface.
Due to the high surface quality requirements of solar aluminum profiles, in order to reduce the pressure of the surface treatment process, but also to ensure the mechanical properties of the profiles, when adjusting the alloying elements, it is necessary to appropriately increase the lower limit of the Cu element, the addition of Cu and unsuitable heat treatment can increase the intergranular corrosion susceptibility of aluminum alloys.
Alloy 6005
For 6005 aluminum alloy, its tensile strength is 280MPa, belonging to the Al-Mg-Si system of medium-strength alloys. 6005 has high process performance, suitable for applications requiring high resistance to corrosion and oxidation, easy to coat, and good processability. However, due to the use of T5 state (state after heat treatment), that is, solid solution treatment plus incomplete artificial aging, 6005 aluminum alloy stored at room temperature for a long time after hot working, has been naturally aging to a basically stable state, the intergranular corrosion susceptibility is weakened, the precipitated phases on the grain boundaries began to grow up, and the gaps between each other have been enlarged, which may have an impact on the hardness and mechanical properties.
In summary, improving the quality of cast rods is an important part of improving the surface quality and mechanical properties of profiles. Adopt the grain refinement process, take effective technical measures to reduce the defects such as slagging, loosening, coarse grain and other defects of cast rods, and homogenize the cast rods. In addition, strengthen the casting of low-fold organization analysis, quality control, reduce the defective casting put into use, which is also to reduce and eliminate the “adsorption particles” effective means.
3. Solar frame aluminum extrusion production process analysis
The common defects in the extrusion production of aluminum profiles for solar frames are more intuitive, such as bending, twisting, deformation, slagging, and so on. Extrusion production of solar aluminum alloy profiles, is the simplest part of the whole production process, choose the best extrusion press, control the three temperatures (extrusion temperature, cast bar heating temperature, die temperature) and extrusion speed, and in the production process, constantly adjust the parameters. Extrusion process control:
- Aluminum bar on the machine temperature 450 ℃ ~ 460 ℃. Aluminum rods can be heated to 500 ℃ ~ 520 ℃, and then removed from the heating furnace to cool down, extrusion bar temperature try not to be too high, to avoid black lines, drag injury palsy phenomenon occurs.
- Mold temperature 450 ℃ ~ 480 ℃, must ensure that in the mold heating furnace heating more than 2h, but more than 8h must be removed from the mold.
- Sheng ingot cylinder temperature 380 ℃ ~ 400 ℃, the current extrusion machine factory, extrusion machine manufacturers will lock the temperature of the ingot cylinder maximum temperature of 400 ℃.
- Extrusion speed depends on the surface quality of the material. In general 8m/min ~ 18m/min outlet online quenching temperature of 520 ± 5 ℃, 6063 alloy online quenching temperature of 515 ± 5 ℃, the cooling rate of 4 ℃ / S (air volume of 660m3 / h full pressure, wind pressure 850Pa).
- The employees who operate the tail section should pay attention to scuffing, scratching, and bruising the profiles in the process of moving the profiles. The profiles should not be overlapped in the framing, and the distance between the support and the support must be kept about 2㎝ to avoid mutual abrasion. Manufacturers who have the condition should separate the profiles layer by layer by using tile purlin paper, and then place the mat strips up and down correspondingly.
Optimization Analysis of Aluminum Profile Mould Design for Solar Frame
The choice of extruder capacity, on the one hand, we should consider the equipment conditions of the production enterprise, on the other hand, we should consider the extrusion coefficient, which can make the extrusion molding smooth and smooth, and also can meet the mechanical properties of the profile. According to this principle, the extrusion coefficient selection of 40 ~ 70 is the most appropriate; extruder selection of 1450 T, 1800 T. The section of Jinko solar frame aluminum profile produced by our factory is shown in the figure below:
526-215 series solar energy frame profile section drawing
Our factory selects 1800T extruder, the inner diameter of the extrusion barrel is Φ185mm, double hole extrusion is used on this machine, the extrusion coefficient is 56, and the external dimension of the adopted mold is Φ260/120 (outer diameter/thickness) mm.
- Mold Requirements
- Sufficient empty knife bit ≥2.5㎜ to ensure that the empty knife bit does not stick to aluminum.
- Surface hardness must reach HV≥1000 with good surface finish.
- The hardness of the mold must reach ≥50HW after heat treatment.
- Mould working belt processing with slow walking wire, high precision requirements, the working belt can not be too long, the length of control between 3mm ~ 8mm, and must ensure that the arc transition, minimize the length of the working belt fall.
- The working belt is strictly prohibited to have a gap, a microfilament is not allowed.
- Work belt polishing should be bright, the last polishing needs to use 1000 mesh metallographic sandpaper, to ensure that the work belt up mirror surface.
- The nitriding interval of the mold should be lower than the number of production branches of ordinary profiles.
