Q1: How do alloying elements alter aluminum's properties?
Copper (2xxx series) enhances strength but reduces corrosion resistance; magnesium (5xxx) improves weldability and marine corrosion resistance; silicon (4xxx) lowers melting points for casting; zinc (7xxx) enables precipitation hardening for aerospace. Manganese (3xxx) strengthens beverage cans without compromising formability. Each element modifies crystal structure, dislocation movement, and precipitate formation.
Q2: What distinguishes wrought vs. cast aluminum alloys?
Wrought alloys (1xxx-8xxx series) are homogenized and rolled/extruded into semi-finished products, requiring high ductility for shaping. Cast alloys (e.g., 356, 380) contain higher silicon (up to 12%) for fluidity in molds. Wrought alloys use temper designations (H1x, T6), while cast alloys specify heat treatment states like F (as-cast) or T6 (solutionized + aged).
Q3: How does T6 tempering strengthen aluminum?
T6 involves solution heat treating at 480-575°C to dissolve alloying elements, then rapid quenching to form a supersaturated solid solution. Artificial aging at 150-200°C precipitates nanoscale phases like Mg₂Si (in 6061) or Al₂CuMg (in 2024). These particles impede dislocation movement, increasing tensile strength up to 300% versus annealed states.
Q4: Why is 6061 alloy termed "structural aluminum"?
6061 (Al-Mg-Si-Cu) balances strength (310 MPa UTS), corrosion resistance, weldability, and machinability. Its T6 temper is ideal for architectural beams, marine frames, and truck chassis. Magnesium silicide precipitates provide age-hardening, while chromium controls grain growth. It's 30% stronger than 6063 extrusion alloy but maintains good anodizing response.
Q5: What enables 7075 alloy's ultra-high strength?
7075 (Al-Zn-Mg-Cu) achieves 570 MPa UTS via fine η' (MgZn₂) precipitates. Zinc content (5.1-6.1%) enables dense precipitate networks. Copper improves stress-corrosion resistance. Used in aircraft spars and military gear, it's 90% stronger than 6061 but less corrosion-resistant, often requiring alclad coatings or anodizing.
