What is pure aluminum?
Pure aluminum is generally defined as aluminum with a purity of 99.0% to 99.9%, and China is defined as aluminum with a purity of 98.8% to 99.7%. Chinese processing industry pure aluminum grades are 1080, 1080A, 1070, 1070A(L1), 1370, 1060(L2), 1050, 1050A(L3), 1A50(LB2), 1350, 1145, 1035(L4), 1A30(L4- 1), 1100 (L5-1), 1200 (L-5), 1235, etc. Iron and silicon are its main impurities and increase according to the number of grades.
The structure of pure aluminum
Industrial pure aluminum can be regarded as an aluminum-iron-silicon alloy with very low content of iron and silicon. In the impurity phase, in addition to acicular hard and brittle FeAl3 and massive hard and brittle silicon particles, two ternary phases can also be formed. When Fe>Si, α(Fe2SiAl8) phase is formed; when Si>Fe, The β(FeSiAl5) phase is formed. Both phases are brittle compounds, the latter being more harmful to plasticity. Therefore, Fe>Si is generally used in industrial pure aluminum. When Fe>Si, it can also narrow the crystallization temperature range and reduce the tendency of casting cracks. When Fe/Si ≥ 2~3, industrial pure aluminum sheets with fine grains and good stamping properties can be produced. It should be pointed out that iron and silicon mostly exist in the form of ternary compounds in industrial pure aluminum, and there are few opportunities for FeAl3 and free silicon to appear.
Industrial pure aluminum has the general characteristics of aluminum, low density, good electrical and thermal conductivity, good corrosion resistance, good plastic processing performance, can be processed into plates, strips, foils and extruded products, etc. spot welding.
Industrial pure aluminum cannot be strengthened by heat treatment, and its strength can be improved by cold deformation. The only form of heat treatment is annealing. The starting temperature of recrystallization is related to the impurity content and degree of deformation, generally around 200 °C. σb=80～100MPa of annealed sheet, σ0.2=30～50MPa, ζ=35%～40%, HB=25～30. After 60%~80% cold deformation, although it can be increased to 150~180MPa, the ζ value has dropped to 1%~1.5%. Increasing the content of iron and silicon impurities can improve the strength, but reduce the plasticity, electrical conductivity and corrosion resistance. The mechanical properties of different cold work hardening states can be obtained by adjusting the annealing temperature after cold deformation or by controlling the amount of cold deformation after annealing.
Types of Pure aluminum
(1) 1A50 industrial pure aluminum
Features and scope of application: It is industrial pure aluminum, with high plasticity, corrosion resistance, electrical conductivity and thermal conductivity, but low strength, heat treatment can not strengthen the machinability; gas welding, hydrogen atom welding and contact welding, not easy to braze Welding; easy to withstand various pressure processing and extension, bending.
Aluminum Al: 99.50
Silicon Si: ≤0.25
Copper Cu: ≤0.05
Magnesium Mg: ≤0.05
Manganese Mn: ≤0.05
Titanium Ti: ≤0.05
Iron Fe: 0.000-0.400
Note: Single: ≤0.03
Tensile strength σb (MPa): ≤137
Elongation δ10 (%): ≤3
(2) 1A99 industrial pure aluminum
Silicon Si: 0.003
Iron Fe: 0.003
Copper Cu: 0.003
Aluminum Al: 99.99
Tensile strength σb/(MPa): 35-100
Elongation (δ10/%): ≥0.5 
Properties of pure aluminum
- (1) Low density: The density of pure aluminum is close to 2700KG/M³, which is about 35% of the density of iron.
(2) It can be strengthened: Although the strength of pure aluminum is not high, it can be more than doubled by cold working. And it can be alloyed by adding magnesium, zinc, copper, manganese, silicon, lithium, scandium and other elements, and then further strengthened by heat treatment, and its strength is comparable to that of high-quality alloy steel.
(3) Easy to process: Aluminum can be cast by any casting method. Aluminum has good plasticity and can be rolled into sheets and foils; drawn into pipes and filaments; extruded into various civilian profiles; and can be machined at the maximum speed that most machine tools can achieve, such as turning, milling, boring, and planing.
(4) Corrosion resistance: On the surface of aluminum and its alloys, it is easy to form a dense and firm AL2O3 protective film. This protective film will only be destroyed under the intense action of halogen ions or alkali ions. Therefore, aluminum has good resistance to atmospheric (including industrial atmosphere and marine atmosphere) corrosion and water corrosion. It can resist the corrosion of most acids and organic substances. The corrosion inhibitor is used to resist the corrosion of weak alkali solution; the corrosion resistance of aluminum alloy can be improved by adopting protective measures.
(5) Good electrical and thermal conductivity: The electrical and thermal conductivity of aluminum is second only to silver, copper and gold. At room temperature, the equivalent volume conductivity of electrical aluminum can reach 62% IACS. If calculated by unit mass conductivity, its conductivity is twice that of copper.
(6) Strong reflectivity: The reflectivity of the polished surface of aluminum to white light is more than 80%, and the higher the purity, the higher the reflectivity. At the same time, aluminum has good reflective properties for infrared, ultraviolet, electromagnetic waves, and thermal radiation.
(7) No magnetism, no sparks when impacted: This is very valuable for some special purposes, such as instrument materials, shielding materials for electrical equipment, flammable and explosive production equipment, etc.
(8) Sound-absorbing: Beneficial for interior decoration, it can also be configured as a damping alloy.
(9) Resistance to nuclear radiation: For high-energy neutrons, aluminum has the same degree of neutron absorption cross-section as other metals. For neutrons in the low-energy range, its absorption cross-section is smaller, second only to metals such as beryllium, magnesium, and zirconium. The biggest advantage of aluminum’s resistance to nuclear radiation is that the induced radiation energy generated by irradiation decays very quickly.
(10) Beautiful: Aluminum and its alloys have a silvery-white luster on the surface due to their strong reflectivity. High finish and brightness can be achieved after machining. If it is anodized and colored, it can not only improve the corrosion resistance, but also obtain colorful and dazzling products. Aluminium is also an excellent substrate for the production of painted materials
- Atom and crystal structure: Atomic number: 13 Valence of elements: 3
Atomic weight: 26.98
Atomic radius: 0.143nm
Lattice type: face-centered cubic lattice
Lattice constant: 0.404nm
No allotropic transformation
Physical properties: Density: 20 degrees (solid state): 2.6996 g/cm3
700 degrees (liquid): 2.371 g/cm3
Melting point: 99.996%AL: 660.24℃; 99.6% AL: 658.7℃
Latent heat of fusion: 388.116 J/g
Specific heat capacity: solid state at room temperature: 0.946 J/(g. K)
Melting point liquid: 1.289 J/(g. K)
Thermal conductivity: 2.177 W/(cm. K)
Linear expansion coefficient: 23.6×10-6
Electrode potential: -1.3V
Mechanical properties: elastic modulus: 69000～71000MPa
Tensile strength: 90～120MPa
Yield strength: 20～90MPa
Brinell hardness: 24-32HB
Impact toughness: 10～20 J/cm2
Chemical properties of pure aluminum
It has good corrosion resistance in fresh water, sea water, air, concentrated nitric acid, nitrate, gasoline, lubricating oil and various organic solvents; it has poor corrosion resistance in alkali, carbonate and dilute acid.
Applications of pure aluminum
Industrial pure aluminum is widely used and can be used as electrical aluminum, such as busbars, wires, cables, electronic parts; heat exchangers, coolers, chemical equipment; packaging supplies for food and medicine such as cigarettes, tea, sugar, beer barrels, etc. Deep-drawn products; used in buildings as roof panels, ceilings, partition walls, sound-absorbing and heat-insulating materials, as well as household utensils, cooking utensils, etc.
Aluminum has a history of more than 100 years since it was discovered by Danish scientist H.C. Oersted in 1825. It has been more than 100 years since the molten salt electrolysis method (Hall-Heroult method) for industrial aluminum extraction was introduced in 1886. For more than 100 years, aluminum and aluminum alloys have been widely used, and aluminum is widely used in various departments of industry and agriculture, aviation, aerospace, defense industry, and even people’s daily life. Aluminum production ranks first in non-ferrous metals, second only to steel production. The reason why aluminum is widely used is that in addition to its rich reserves (about 8.2% of the mass of the earth’s crust, which is the most widely distributed metal element in the earth’s crust), and its relatively simple smelting, it is more important that aluminum has a series of excellent properties.
Effects of Rare Earth Elements on Electrical Conductivity of Industrial Pure Aluminum
(1) Mixed rare earth M2RE (50%Ce + 23%La) did not improve the electrical conductivity of industrial pure aluminum.
(2) The pure rare earth elements lanthanum and cerium have obvious improvement effects on the electrical conductivity of industrial pure aluminum L2 and L3, and when the content of lanthanum and cerium is less than 1.5%, this effect increases with the increase of rare earth content, and the content exceeds this. range, the resistivity has an upward trend.
(3) The addition of rare earth elements lanthanum and cerium slightly increases the high temperature resistivity of aluminum.
(4) The addition of rare earth elements lanthanum and cerium can change the distribution of impurity elements in aluminum, especially silicon can be transformed from solid solution state to precipitation state, thereby reducing the adverse effect of silicon on aluminum conductivity.