The density of titanium alloy is about 4.5, and the density of aluminum alloy is about 2.7. Titanium alloys of the same size are slightly heavier. Titanium alloy has high strength, good corrosion resistance and high heat resistance. The density of titanium alloy is generally about 4.51g/cubic centimetre, which is only 60% of steel. The density of pure titanium is close to that of ordinary steel. Some high-strength titanium alloys exceed the strength of many alloy structural steels. Aluminum alloy has low density, but relatively high strength, close to or exceeds high-quality steel, good plasticity, can be processed into various profiles, has excellent electrical conductivity, thermal conductivity and corrosion resistance, widely used in industry, the amount of use is second only to steel.
Titanium alloy is an alloy composed of titanium added with other elements. Titanium has two kinds of heterogeneous crystals: below 882 ℃ is close-packed hexagonal structure α titanium, above 882 ℃ is body-centred cubic β titanium.
Alloying elements can be divided into three categories according to their influence on the phase transition temperature:
①The elements that stabilize the α phase and increase the phase transition temperature are α stable elements, including aluminum, carbon, oxygen and nitrogen. Among them, aluminum is the main alloy element of titanium alloy, which has obvious effects on improving the normal temperature and high temperature strength of the alloy, reducing the specific gravity, and increasing the elastic modulus.
②The element that stabilizes the β phase and lowers the phase transition temperature is the β stable element, and can be divided into two types: isomorphic and eutectoid. The former has molybdenum, niobium, vanadium, etc.; the latter has chromium, manganese, copper, iron, silicon, etc.
③ Elements that have little effect on the phase transition temperature are neutral elements, such as zirconium and tin.
Oxygen, nitrogen, carbon and hydrogen are the main impurities of titanium alloys. Oxygen and nitrogen have greater solubility in the α phase, which has a significant strengthening effect on titanium alloys, but reduces the plasticity. Generally, the content of oxygen and nitrogen in titanium is 0.15 to 0.2% and 0.04 to 0.05%, respectively. The solubility of hydrogen in the α phase is very small. Too much hydrogen dissolved in the titanium alloy will produce hydrides, making the alloy brittle. Usually the hydrogen content in titanium alloy is controlled below 0.015%. The dissolution of hydrogen in titanium is reversible and can be removed by vacuum annealing.
Aluminum alloy has better physical and mechanical properties than pure aluminum, easy to process, high durability, wide application range, good decorative effect and rich color. Aluminum alloys are divided into rust-proof aluminum, hard aluminum, super hard aluminum and other types. Each type has its own use range and has its own code for users to choose. Aluminum alloy still maintains the characteristics of light weight, but the mechanical properties are significantly improved.
Aluminum alloy has low density, but relatively high strength, close to or exceeds high-quality steel, good plasticity, can be processed into various profiles, has excellent electrical conductivity, thermal conductivity and corrosion resistance, widely used in industry, the amount of use is second only to steel . Some aluminum alloys can use heat treatment to obtain good mechanical properties, physical properties and corrosion resistance.
The hard aluminum alloy belongs to the AI-Cu-Mg series and generally contains a small amount of Mn, which can be strengthened by heat treatment. It is characterized by high hardness, but poor plasticity. Super hard aluminum belongs to the Al-Cu-Mg-Zn series, can be heat-treated and strengthened, and is the aluminum alloy with the highest strength at room temperature, but has poor corrosion resistance and fast softening at high temperature. Forged aluminum alloys are mainly Al-Zn-Mg-Si series alloys. Although there are many kinds of added elements, but the content is small, so they have excellent thermoplasticity and are suitable for forging, so they are also called forged aluminum alloys.
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