6063 aluminum alloy
6063 aluminum alloy is widely used as a frame for building aluminum doors, windows, and curtain walls, and is a common type of aluminum alloy. In order to ensure that doors, windows, and curtain walls have high wind resistance, assembly performance, corrosion resistance, and decorative performance, the requirements for the comprehensive performance of aluminum alloy profiles are much higher than industrial profile standards.
6063 aluminum alloy is widely used in the frames of building aluminum doors, windows, and curtain walls. In order to ensure that doors, windows, and curtain walls have high wind pressure resistance, assembly performance, corrosion resistance, and decorative performance, the requirements for the comprehensive performance of aluminum alloy profiles are much higher than those of industrial profile standards. Within the composition range of 6063 aluminum alloy specified in the national standard GB/T3190, different values of chemical composition will result in different material properties. When the chemical composition range is large, the performance differences will fluctuate within a large range, making it difficult to control the comprehensive performance of the profile.
chemical composition
The chemical composition of 6063 aluminum alloy has become an important part of producing high-quality aluminum alloy building profiles.
The impact of performance
6063 aluminum alloy is a heat treatable strengthening alloy with moderate strength in the AL Mg Si system. Mg and Si are the main alloying elements, and the main task of optimizing the chemical composition is to determine the percentage content (mass fraction, the same below) of Mg and Si.
The role and influence of Mg on the composition of Mg and Si in the strengthening phase Mg2Si. The higher the content of Mg, the more Mg2Si there is, and the greater the strengthening effect of heat treatment. The tensile strength of the profile is also higher, but the deformation resistance also increases. The plasticity of the alloy decreases, the processing performance deteriorates, and the corrosion resistance deteriorates.
The effect and influence of 1.2Si should be such that all Mg in the alloy can exist in the form of Mg2Si phase to ensure that the effect of Mg is fully utilized. As the Si content increases, the grain size of the alloy becomes finer, the metal flowability increases, the casting performance improves, the heat treatment strengthening effect increases, the tensile strength of the profile increases while the plasticity decreases, and the corrosion resistance deteriorates.
Selection of Content
2.1 Determination of Mg2Si content
2.1.1 The role of Mg2Si phase in alloys Mg2Si can dissolve or precipitate with temperature changes and exist in different forms in alloys: (1) The Mg2Si phase dispersed particles precipitated in the dispersed phase β '' solid solution are an unstable phase that grows with increasing temperature. (2) The transitional phase β 'is an intermediate metastable phase formed by the growth of β' ', which also grows with increasing temperature. (3) The precipitate phase β is a stable phase formed by the growth of β 'phase, which tends to aggregate at grain boundaries and dendritic boundaries. The Mg2Si phase can have a strengthening effect when it is in a dispersed β '' phase state, and the process of transforming the β phase into the β '' phase is the strengthening process, while the opposite is the softening process.
The heat treatment strengthening effect of 6063 aluminum alloy increases with the increase of Mg2Si content. When the amount of Mg2Si is within the range of 0.71% to 1.03%, its tensile strength increases approximately linearly with the increase of Mg2Si amount, but the deformation resistance also increases, making processing difficult. When the amount of Mg2Si is less than 0.72%, there is a risk that the tensile strength value of products with a low extrusion coefficient (less than or equal to 30) may not meet the standard requirements. When the amount of Mg2Si exceeds 0.9%, the plasticity of the alloy tends to decrease. The GB/T5237.1-2000 standard requires that the σ b of 6063 aluminum alloy T5 state profiles be ≥ 160MPa, and the σ b of T6 state profiles be ≥ 205MPa. Practice has shown that the tensile strength of this alloy can reach 260MPa. But there are many factors that affect mass production, and it is impossible to guarantee that they will all reach such a high level. Taking into account all factors, profiles should not only have high strength to ensure that the product meets standard requirements, but also make the alloy easy to extrude, which is beneficial for improving production efficiency. When designing the alloy strength, we take 200MPa as the design value for profiles delivered in T5 state. From Figure 1, it can be seen that when the tensile strength is around 200MPa, the amount of Mg2Si is approximately 0.8%. However, for the T6 state profile, we take the design value of tensile strength as 230 MPa, and at this point, the amount of Mg2Si increases to 0.95%.
Once the amount of Mg2Si is determined, the Mg content can be calculated according to the following formula: Mg%=(1.73 × Mg2Si%)/2.73
2.1.4 Determination of Si Content: The Si content must meet the requirement that all Mg forms Mg2Si. Due to the relative atomic mass ratio of Mg to Si in Mg2Si being Mg/Si=1.73, the basic Si content is Si based=Mg/1.73. However, practice has shown that when using Si based ingredients, the tensile strength of the produced alloy is often low and unqualified. Obviously, it is due to the insufficient amount of Mg2Si in the alloy. The reason is that impurity elements such as Fe and Mn in the alloy compete for Si, for example, Fe can form ALFeSi compounds with Si. So, there must be excess Si in the alloy to compensate for the loss of Si. Excess Si in alloys can also supplement the improvement of tensile strength. The increase in tensile strength of the alloy is the sum of the contributions of Mg2Si and excess Si. When the Fe content in the alloy is high, Si can also reduce the adverse effects of Fe. However, due to the fact that Si can reduce the plasticity and corrosion resistance of alloys, it should be reasonably controlled. Based on practical experience, our factory believes that it is better to choose an excess Si content within the range of 0.09% to 0.13%. The Si content in the alloy should be: Si%=(Si based+Si excess)%
Control range
The control range of 3.1Mg is that Mg is a flammable metal and may be burned during melting operations. When determining the control range of Mg, the error caused by burning should be considered, but it should not be too wide to prevent the alloy properties from losing control. We have controlled the fluctuation range of Mg within 0.04% based on our experience and the level of ingredients, melting, and testing in our factory. For T5 profiles, we have taken 0.47% to 0.50%, and for T6 profiles, we have taken 0.57% to 0.60%.
Once the range of Mg is determined, the control range of Si can be determined by the Mg/Si ratio. Because the factory controls Si to be between 0.09% and 0.13%, Mg/Si should be controlled between 1.18 and 1.32. The selection range of chemical composition for T5 and T6 state profiles of 3.36063 aluminum alloy. When changing the alloy composition, such as increasing the amount of Mg2Si to 0.95% to facilitate the production of T6 profiles, Mg can be moved up to around 0.6% along the upper and lower limits of Si. At this point, Si is about 0.46%, Si is 0.11%, and Mg/Si is 1.3%
Based on our factory's experience, controlling the amount of Mg2Si in 6063 aluminum alloy profiles within the range of 0.75% to 0.80% can fully meet the requirements of mechanical properties. Under normal extrusion coefficient (greater than or equal to 30), the tensile strength of the profile is within the range of 200-240 MPa. By controlling the alloy in this way, not only does the material have good plasticity, easy extrusion, high corrosion resistance, and good surface treatment performance, but it can also save alloy elements. However, special attention should be paid to strict control of impurity Fe. If the Fe content is too high, it will increase the extrusion force, deteriorate the surface quality of the extruded material, increase the color difference of anodizing, and make the color dull and dull. Fe also reduces the plasticity and corrosion resistance of the alloy. Practice has proven that controlling the Fe content within the range of 0.15% to 0.25% is quite ideal.
chemical composition
Silicon Si: 0.20-0.6
Iron Fe: 0.35
Copper Cu: 0.10
Manganese Mn: 0.10
Magnesium Mg: 0.45-0.9
Chromium Cr: 0.10
Zinc Zn: 0.10
Titanium Ti: 0.10
Aluminum Al: Excess
other:
Individual: 0.05 Total: 0.15
Mechanical properties:
Tensile strength σ b (MPa): ≥ 205
Tensile stress σ p0.2 (MPa): ≥ 170
Elongation rate δ 5 (%): ≥ 7
Note: Longitudinal mechanical properties of bar at room temperature
Sample size: diameter ≤ 12.5
Surface corrosion phenomenon
The corrosion behavior of 6063 aluminum alloy profiles caused by silicon can be completely prevented and controlled. As long as the procurement of raw materials and alloy composition are effectively controlled, the magnesium silicon ratio is ensured to be within the range of 1.3-1.7, and the parameters of each process are strictly controlled to avoid silicon segregation and dissociation, and to form a beneficial Mg2Si strengthening phase between silicon and magnesium as much as possible.
If this phenomenon of silicon corrosion points is found, special attention should be paid during surface treatment. During the degreasing and degreasing process, weak alkaline bath solution should be used as much as possible. If conditions do not allow, the soaking time in acidic degreasing solution should be shortened as much as possible (qualified aluminum alloy profiles can be placed in acidic degreasing solution for 20-30 minutes without any problem, while problematic profiles can only be placed for 1-3 minutes). In addition, the pH value of the washing water should be higher in the future (pH>4, Cl - content should be controlled). During the alkaline corrosion process, the corrosion time should be extended as much as possible. When neutralizing and releasing light, nitric acid light solution should be used. During sulfuric acid anodizing, electric oxidation treatment should be carried out as soon as possible. In this way, dark gray corrosion points caused by silicon should be treated as soon as possible. It's not obvious, but it can meet the usage requirements.
Spot specifications
6063 sheet stock specifications: 0.3mm-350mm (thickness)
6063 rod stock specifications: 3.0mm-500mm (diameter)
6063 wire stock specifications: 0.1mm-20mm (wire diameter)