China Aluminum Industry Network
(1) Aluminum has a strong affinity with oxygen in the air, readily forming a dense and tough aluminum oxide layer that is approximately 0.1 micrometers thick. This oxide film has a melting point of up to 2050°C, which is much higher than that of aluminum itself. Its density is about 1.4 times that of aluminum. During welding, this oxide layer can prevent proper bonding between metals, leading to slag inclusion. Additionally, the oxide film absorbs moisture, which can result in porosity during the welding process. These defects negatively impact the performance of the welded joint. To ensure quality, it's essential to thoroughly clean the surface of the workpiece before welding and protect it from re-oxidation during the process. Effective protection of molten metal and high-temperature areas is crucial in welding aluminum and its alloys. Common protective measures include mechanical grinding or chemical cleaning (such as D40 solution) to remove oxides from the weld area, and using high-purity shielding gases like 99.99% argon during the welding process. (2) Aluminum has high thermal conductivity and specific heat capacity. Although its melting point is much lower than that of steel, its thermal conductivity and specific heat are more than twice as high. This means a large amount of heat is quickly conducted into the surrounding metal. To achieve high-quality welds, concentrated and powerful heat sources are required. For plates thicker than 8 mm, preheating and other techniques are necessary to ensure proper fusion. (3) The linear expansion coefficient of aluminum alloys is roughly twice that of steel, and their volumetric shrinkage rate during solidification is around 6.5% to 6.6%. This makes them prone to distortion during welding. To reduce deformation, suitable welding tools and optimized process parameters and sequences should be used, especially when welding thin plates. Some aluminum alloys tend to form hot cracks in the weld metal and liquidation cracks in the heat-affected zone, often due to excessive internal stress within the brittle temperature range. Hot cracking is a common serious defect in high-strength aluminum alloys. Preventive measures include improving joint design, selecting appropriate welding parameters, and using filler materials compatible with the base material. (4) Porosity is a common issue in the welding of aluminum and its alloys, particularly with pure aluminum and corrosion-resistant aluminum. Hydrogen is the main cause of porosity, often coming from moisture in the arc atmosphere, welding materials, and moisture absorbed by the base material. Moisture on the oxide film of the welding wire and base material plays a significant role in pore formation. Molten aluminum easily absorbs gas, and as it solidifies, the solubility of the gas decreases rapidly, leading to the formation of pores. To prevent this, strict control over hydrogen sources is essential. Welding materials, including wires, rods, flux, and shielding gas, must be kept dry and free from moisture. Cleaned base metals and wires should be welded within 2–3 hours for best results. During TIG welding, a high current and fast speed are recommended, while MIG welding benefits from a slower speed and higher current to maintain a stable molten pool. (5) At high temperatures, aluminum loses strength significantly. At 370°C, its strength drops to only 10 MPa, making it difficult to support the molten metal during welding. This can lead to poor weld formation, collapse, or burn-through. To address this, backing plates are often used when welding aluminum and its alloys. (6) One challenge in welding aluminum is that it doesn't change color when melting, making it hard for operators to determine the correct temperature. This requires experienced welders who can accurately control the heating process. It's also advisable to use flat welding positions and guide the arc onto a starting/ending plate to improve control and quality.Ceiling lights are a common lighting device with characteristics and attributes such as bright and uniform, space saving, safety and reliability, diversified design, energy conservation and environmental protection, dimming function, and intelligent control
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