Aluminum is the most abundant metallic element in the Earth's crust at approximately 8.2% by weight, yet its widespread use dates only to the late 19th century owing to the difficulty of extracting it from bauxite ore. The Hall-Heroult process, developed simultaneously and independently by Charles Martin Hall in the United States and Paul Heroult in France in 1886, uses electrolysis to reduce alumina into metallic aluminium. Today, global primary aluminium production exceeds 65 million tonnes per year.
6061 vs 6063: Structural vs Architectural
Alloy 6061 and 6063 dominate the aluminium extrusion market but serve different purposes. Both belong to the 6xxx series, where magnesium and silicon form the hardening precipitate Mg2Si during artificial ageing.
Alloy 6061 in the T6 temper achieves a tensile strength of approximately 310 MPa with a yield strength around 276 MPa. This makes it a true structural aluminium, specified for bridges, truck frames, marine components, and heavy-duty industrial equipment. Its silicon content ranges from 0.4% to 0.8%, with magnesium between 0.8% and 1.2%. Weldability is excellent with both TIG and MIG processes, though welding reduces strength in the heat-affected zone by roughly 30%, requiring careful joint design.
Alloy 6063, often called architectural aluminium, prioritises surface finish over ultimate strength. Its tensile strength in the T5 temper reaches roughly 185 MPa, adequate for window frames, door sections, curtain wall mullions, and interior trim but insufficient for primary structural loading. The lower magnesium content, 0.45% to 0.9%, produces a finer grain structure that responds beautifully to anodising. A clear anodised 6063 extrusion can achieve a near-mirror finish that remains stable for decades outdoors.
Anodising
Anodising is an electrochemical process that thickens the natural aluminium oxide layer from a few nanometres to anywhere between 5 and 25 microns for architectural work. The aluminium component serves as the anode in a sulphuric acid bath, where controlled current builds a transparent, hexagonal-pore oxide structure. Dyes absorbed into these pores before sealing produce colours ranging from champagne gold to deep bronze to black. The process adds negligible weight while dramatically improving scratch resistance and eliminating the grey oxidation rub-off that bare aluminium leaves on hands and clothing.
Recycling and Energy
Aluminium recycling is one of the most compelling sustainability stories in materials science. Primary smelting consumes approximately 15 kWh of electricity per kilogram of aluminium produced, while remelting scrap requires only about 0.75 kWh/kg, or roughly 5% of primary energy. This energy differential, combined with the fact that aluminium can be recycled indefinitely without quality loss, means that roughly 75% of all aluminium ever produced remains in use today. The building sector accounts for about 25% of aluminium consumption, with window frames, curtain walling, roofing, and structural glazing systems all contributing. Closed-loop recycling, where post-consumer scrap returns directly to similar products, is increasingly common in Europe, where building deconstruction protocols separate aluminium components at end of life.