[China Aluminum Network] The eight key elements that influence the performance of aluminum alloys are vanadium, calcium, lead, tin, antimony, bismuth, sodium, and others. These elements are typically not processed during the manufacturing of finished aluminum coils due to their different applications. Each of these impurity elements has unique melting points, structural characteristics, and forms various compounds with aluminum, resulting in different impacts on the alloy's properties.
1. Copper: As a significant alloying element, copper contributes to solid-solution strengthening. During aging, CuAl2 precipitates provide additional strengthening. The optimal copper content in aluminum plates usually ranges from 2.5% to 6.8%, with most hard aluminum alloys falling within this range for maximum strength enhancement.
2. Silicon: In Al-Mg2Si-based alloys, silicon exhibits good solubility in aluminum, reaching up to 1.85%. It is commonly used in welding materials and can offer some strengthening effects when added to aluminum. However, its impact on deformation alloys is limited compared to other elements.
3. Magnesium: Magnesium significantly enhances the strength of aluminum alloys. For every 1% increase in magnesium, tensile strength can rise by approximately 34 MPa. Adding small amounts of manganese can further improve the strengthening effect while reducing hot cracking tendencies. Manganese also helps form uniform Mg5Al8 precipitates, improving corrosion resistance and weldability.
4. Manganese: Manganese has a solubility of up to 1.82% in solid solutions. Its addition increases alloy strength, and at a content of 0.8%, elongation reaches a high level. Al-Mn alloys are non-heat-treatable and exhibit short aging times.
5. Zinc: In Al-Zn systems, zinc shows high solubility in aluminum at elevated temperatures (up to 31.6% at 275°C), but this decreases significantly at lower temperatures. While zinc can strengthen deformed alloys, it also increases stress corrosion cracking risks, limiting its use in certain applications.
6. Iron and Silicon: Both elements are common impurities in aluminum alloys. Their interaction determines the formation of different phases such as β-FeSiAl3 or α-Fe2SiAl8. Imbalanced ratios can lead to cracks or brittleness in castings. Proper control of iron and silicon levels is crucial for maintaining mechanical properties and casting quality.
7. Titanium and Boron: Titanium is often added as an Al-Ti or Al-Ti-B master alloy. It forms TiAl2 and acts as a nucleation site during crystallization, refining the microstructure. With boron, the effective titanium content can be reduced to as low as 0.01%.
8. Chromium and Niobium: Chromium forms intermetallics like (CrFe)Al7, which hinder recrystallization and enhance strength. It also improves toughness and reduces cracking sensitivity. However, excessive chromium can affect anodizing. Niobium, when added to high-silicon alloys, refines primary silicon particles, improving ductility and processing performance. It significantly boosts mechanical properties, increasing tensile and yield strengths while enhancing elongation.
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