Classification of Aluminum and Aluminum Alloy Materials (I)

Based on chemical composition and manufacturing processes, aluminum and aluminum alloy materials are classified as follows:

1. Pure Aluminum

1.1 High-purity aluminum. The mass fraction of aluminum in high-purity aluminum is no less than 99.999%. It is mainly used in manufacturing high-purity aluminum alloys, conductive components for the electronics industry, laser materials, and high-precision scientific research equipment due to its ultra-low impurity content. 

1.2 Commercial pure aluminum. The mass fraction of aluminum in commercial pure aluminum exceeds 99%, with common grades such as 1050 (99.5% aluminum content) and 1100 (99.0% aluminum content). Its melting point is 660°C, with no color change during melting. A dense oxide film forms easily on its surface, granting excellent corrosion resistance—a key advantage for applications in humid or mild corrosive environments. The thermal conductivity of pure aluminum is approximately 5 times that of low-carbon steel, and its linear expansion coefficient is about 2 times that of low-carbon steel, making it ideal for heat dissipation components like radiators. Pure aluminum has low strength and is unsuitable as a structural material: the tensile strength of annealed aluminum sheets ranges from 60 to 100MPa, with an elongation of 35% to 40%. 

2. Aluminum Alloys

Aluminum alloys are materials produced by smelting pure aluminum with added alloying elements, aiming to enhance strength and achieve other desired properties. Based on process performance, they are categorized into wrought aluminum alloys and cast aluminum alloys. 

2.1 Wrought Aluminum Alloys 

Wrought aluminum alloys have a single-phase solid solution structure and strong deformability, suitable for forging and rolling. They are divided into non-heat-treatable strengthened aluminum alloys and heat-treatable strengthened aluminum alloys. 

2.1.1 Non-heat-treatable strengthened aluminum alloy. These primarily include Al-Mn and Al-Mg alloys, with typical grades such as 3003 (Al-Mn series) and 5052 (Al-Mg series). Their mechanical properties are improved through solid solution strengthening and work hardening via added manganese and magnesium—they cannot be strengthened by heat treatment but offer higher strength than pure aluminum. Characterized by moderate strength, excellent corrosion resistance, plasticity, and pressure processing performance, they boast the best weldability among aluminum alloys, making them the most widely used in aluminum alloy welded structures, such as ship hulls, pressure vessels, and automotive fuel tanks. 

2.1.2 Heat-treatable strengthened aluminum alloys. These can be enhanced via solution treatment, quenching, and aging processes, mainly including duralumin, super-hard aluminum, and forged aluminum. Heat treatment significantly improves their tensile strength, but they have poor weldability—fusion welding tends to cause cracks, and welded joint strength (especially tensile strength) drops sharply. 

– Duralumin grades are ordered by increasing copper content, with typical grades like 2024. Copper is its main component, usually controlled at 4.0%–4.8% for high strength. Manganese eliminates iron’s adverse effect on corrosion resistance, refines grains, and accelerates age hardening. Elements like Cu, Si, and Mg form aluminum-soluble compounds, enhancing heat treatment strengthening. Annealed duralumin has a tensile strength of 160–220MPa, rising to 312–460MPa after quenching and aging. Due to poor corrosion resistance, a layer of commercial pure aluminum is often cladded on its surface as protection, widely used in aircraft skin and structural frames. 

– Super-hard aluminum. It contains Zn, Mg, and Cu with a total mass fraction of 9.7%–13.5%, with typical grades like 7075. It is the strongest (tensile strength 500–600MPa) and most used light alloy in aerospace, applied in airframe frames, landing gear parts, and high-stress components. However, it has poor plasticity and weldability—welded joints are much weaker than the base metal. High zinc content increases the risk of intergranular corrosion and welding hot cracks. 

– Forged aluminum. It can be strengthened via quenching-aging. It has good high-temperature plasticity (better with lower copper content), suitable for forging and stamping aircraft engine blades, automotive wheels, and machinery parts. Its moderate strength and excellent corrosion resistance ensure wide industrial use. 

2.2 Cast Aluminum Alloys 

These include Al-Si, Al-Cu, Al-Mg, and Al-Zn alloys, with Al-Si alloys being the most widely used. Their eutectic structure ensures good fluidity, granting excellent castability, along with good corrosion resistance, heat resistance, machinability, and weldability. They are commonly used in manufacturing auto engine blocks, transmission housings, and internal combustion engine pistons due to their superior casting performance.