For consumer products, commonly used alloy materials include aluminum alloy, zinc alloy, and magnesium alloy. Titanium alloy is commonly used in the medical field due to its good biocompatibility. This article will explore the characteristics of these alloy materials and make a comparison.

Among these four alloys, titanium alloy is the hardest and has the highest strength. In terms of hardness, titanium alloy is much harder than the other three alloys. In terms of tensile strength, titanium alloy is stronger than zinc alloy, followed by magnesium alloy, and aluminum alloy has the lowest strength.

But in terms of product structure design, weight also needs to be considered. If the specific gravity is taken into account, zinc alloy has the highest density but the lowest specific strength. Titanium alloy and magnesium alloy have higher strength than magnesium alloy, but titanium alloy is expensive and has poor processing performance. Therefore, magnesium alloy is often used in structural components that require comprehensive consideration of weight and strength.

Magnesium and magnesium alloys

Magnesium has a low density and is easy to burn due to its physical and chemical properties. At 20 ℃, the density of metallic magnesium is 1.738g/cm3, and the density of liquid metallic magnesium is 1.58g/cm3; At standard atmospheric pressure, the melting point of magnesium metal is (650 ± 1) ℃, and its boiling point is 1090 ℃. When heated in air, magnesium metal begins to burn between 632 ℃ and 635 ℃. Therefore, the preparation of magnesium and the alloy smelting process are relatively complex. The purity of industrial magnesium can reach 99.9%, but pure magnesium cannot be used as a structural material. Magnesium alloys formed by adding elements such as aluminum, zinc, lithium, manganese, zirconium, and rare earths to pure magnesium have high strength. Currently, magnesium aluminum alloys are the most widely used, followed by magnesium manganese alloys and magnesium zinc zirconium alloys. Mainly used in industrial sectors such as aviation, aerospace, transportation, chemical industry, rockets, etc.

Characteristics of magnesium alloys

① Lightweight.

② Strength. Magnesium alloys have excellent strength to weight ratios in engineering materials such as metals and plastics. The yield strength is 160MPa and the tensile strength is 240MPa.

③ Die casting properties. Under good structural conditions, magnesium alloys allow for a minimum casting wall thickness of 0.6mm, which is something that plastics cannot achieve at the same strength.

④ Shock absorption. Magnesium has excellent hysteresis and shock absorption properties, which can absorb vibration and noise. When used as an equipment casing, it can reduce noise transmission, prevent impact, and prevent dent damage. As a backplane for LCD or LED, it is good.

⑤ Rigid. The rigidity of magnesium is twice that of aluminum and higher than most plastics. Magnesium has good stress resistance.

⑥ High electromagnetic interference barrier. Magnesium alloy has good electromagnetic wave blocking function and is suitable for producing electronic products.

⑦ Good cutting performance

⑧ The specific heat capacity of magnesium alloy is relatively small, and the cooling rate of the alloy liquid is fast.

⑨ Magnesium alloy has a low affinity with mold steel and is not easy to adhere to the mold.

Advantages of magnesium alloy materials

① Lightweight

Magnesium alloy has the lightest specific gravity among all structural alloys, with a specific gravity of 68% for aluminum alloy, 27% for zinc alloy, and 23% for steel. In addition to being used as the shell and internal structural components of 3C products, it is also an excellent material for automotive, aircraft, and other parts.

② Higher specific strength and stiffness

The specific strength of magnesium alloy is significantly higher than that of aluminum alloy and steel, and its specific stiffness is comparable to that of aluminum alloy and steel, but much higher than that of engineering plastics, which is 10 times that of general plastics.

③ Good vibration resistance

Under the same load, the vibration damping performance is 100 times that of aluminum and 300-500 times that of titanium alloy.

④ Excellent electromagnetic shielding performance

The casing of 3C products (mobile phones and computers) should provide superior electromagnetic protection, while the magnesium alloy casing can fully absorb electromagnetic interference with frequencies exceeding 100db.

⑤ Good heat dissipation

The thermal conductivity of general metals is hundreds of times that of plastics, while the thermal conductivity of magnesium alloys is slightly lower than that of aluminum alloys and copper alloys, and much higher than that of titanium alloys. Its specific heat is close to that of water and is the highest among commonly used alloys.

⑥ Good texture

The appearance and tactile texture of magnesium alloy are excellent, making the product more luxurious.

⑦ Good recyclability

As long as it costs 4% of the price of new materials, magnesium alloy products and waste can be recycled and reused.

⑧ Stable resource provision

Magnesium ranks eighth in reserves in the Earth's crust, with most of its raw materials extracted from seawater, making its resources stable and abundant.

aluminium alloy

The general term for alloys based on aluminum. The main alloying elements are copper, silicon, magnesium, zinc, manganese, and the secondary alloying elements are nickel, iron, titanium, chromium, lithium, etc.

Aluminum alloy has low density but high specific strength, approaching or exceeding high-quality steel, good plasticity, and can be processed into various profiles. It has excellent conductivity, thermal conductivity, and corrosion resistance, and is widely used in industry, with a usage rate second only to steel.

Aluminum alloy classification

Aluminum alloys are divided into two categories: cast aluminum alloys, used in the as cast state; Deformed aluminum alloy, capable of withstanding pressure processing, with mechanical properties higher than as cast state. Can be processed into various forms and specifications of aluminum alloy materials. Mainly used for manufacturing aviation equipment, daily necessities, building doors and windows, etc.

Aluminum alloy processing methods

Aluminum alloys can be divided into deformed aluminum alloys and cast aluminum alloys according to processing methods. Deformable aluminum alloys are divided into non heat treatable reinforced aluminum alloys and heat treatable reinforced aluminum alloys. The non heat treatment strengthening type cannot improve mechanical properties through heat treatment, and can only be strengthened through cold processing deformation. It mainly includes high-purity aluminum, industrial high-purity aluminum, industrial pure aluminum, and rust proof aluminum. Heat treatable reinforced aluminum alloys can improve their mechanical properties through heat treatment methods such as quenching and aging. They can be divided into hard aluminum, forged aluminum, ultra hard aluminum, and special aluminum alloys.

Aluminum alloys can achieve good mechanical, physical, and corrosion resistance properties through heat treatment.

Casting aluminum alloys can be divided into aluminum silicon alloys, aluminum copper alloys, aluminum magnesium alloys, and aluminum zinc alloys according to their chemical composition.

kirsite

The grade of zinc based alloy material commonly used for electroplating is ZnAl 4-1, with a composition (%) of Al 3.5-4 9 , Cu 0.75～1.25, Mg 0.03～0.08,  The remaining amount is Zn.

① Relatively significant

② Good casting performance, capable of die-casting complex and thin-walled precision parts, with a smooth casting surface

③ Surface treatment available: electroplating, spraying, spray painting

④ During melting and die casting, it does not absorb iron, does not corrode the mold, and does not stick to the mold

⑤ Has excellent mechanical properties and wear resistance at room temperature

⑥ Low melting point, melts at 385 ℃, easy to die cast into shape

Issues to be noted during use

① Poor corrosion resistance.

When the impurity elements lead, cadmium, and tin in the alloy composition exceed the standard, it leads to aging and deformation of the casting.

② Time effect

The microstructure of zinc alloys is mainly composed of zinc rich solid solutions containing Al and Cu and Al rich solid solutions containing Zn, and their solubility decreases with decreasing temperature. However, due to the extremely fast solidification rate of die-casting parts, the solubility of the solid solution is greatly saturated at room temperature. After a certain period of time, this supersaturation phenomenon will gradually dissipate, causing slight changes in the shape and size of the casting.

③ Zinc alloy die castings should not be used in working environments with high and low temperatures (below 0 ℃).

titanium alloy

Titanium alloy is an alloy composed of titanium as the base and other elements added. Titanium has two types of homogeneous and heterogeneous crystals: alpha titanium with a close packed hexagonal structure below 882 ℃, and beta titanium with a body centered cubic structure above 882 ℃.

Alloy elements can be classified into three categories based on their influence on the phase transition temperature:

① The elements that stabilize the alpha phase and increase the phase transition temperature are alpha stable elements, such as aluminum, carbon, oxygen, and nitrogen. Aluminum is the main alloying element in titanium alloys, which has a significant effect on improving the room temperature and high temperature strength, reducing the specific gravity, and increasing the elastic modulus of the alloy.

② The elements that stabilize the β phase and lower the phase transition temperature are β - stable elements, which can be divided into two types: eutectic and eutectoid. The former includes molybdenum, niobium, vanadium, etc; The latter includes 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.

Characteristics of titanium alloy

Titanium is a new type of metal, and its properties are related to the impurity content of carbon, nitrogen, hydrogen, oxygen, etc. The purest titanium iodide impurity content does not exceed 0.1%, but its strength is low and its plasticity is high.

① High intensity

The density of titanium alloy is generally around 4.51g/cubic centimeter, which is only 60% of that of steel. The density of pure titanium is close to that of ordinary steel, and some high-strength titanium alloys exceed the strength of many alloy structural steels. Therefore, the specific strength (strength/density) of titanium alloy is much higher than other metal structural materials, which can produce components with high unit strength, good rigidity, and light weight. The engine components, skeleton, skin, fasteners, and landing gear of the aircraft are all made of titanium alloy.

② High thermal intensity

The use temperature is several hundred degrees higher than that of aluminum alloy, and it can still maintain the required strength at moderate temperatures. It can work for a long time at temperatures of 450-500 ℃. These two types of titanium alloys still have high specific strength in the range of 150 ℃ to 500 ℃, while aluminum alloy shows a significant decrease in specific strength at 150 ℃. The working temperature of titanium alloy can reach 500 ℃, while that of aluminum alloy is below 200 ℃.

③ Good corrosion resistance

Titanium alloys work in humid atmospheres and seawater media, and their corrosion resistance is much better than stainless steel; Has particularly strong resistance to pitting corrosion, acid corrosion, and stress corrosion; Has excellent corrosion resistance to alkali, chloride, organic substances such as chlorine, nitric acid, sulfuric acid, etc. However, titanium has poor corrosion resistance to reducing oxygen and chromium salt media.

④ Good low-temperature performance

Titanium alloys can maintain their mechanical properties at low and ultra-low temperatures. Titanium alloys with good low-temperature performance and extremely low interstitial elements, such as TA7, can maintain a certain degree of plasticity at -253 ℃. Therefore, titanium alloy is also an important low-temperature structural material.

⑤ High chemical activity

Titanium has high chemical activity and reacts strongly with oxygen, nitrogen, titanium alloy products, CO, CO2, water vapor, ammonia, and other substances in the atmosphere. When the carbon content is greater than 0.2%, hard TiC will form in the titanium alloy; When the temperature is high, the interaction with N will also form a TiN hard surface layer; At temperatures above 600 ℃, titanium absorbs oxygen to form a hardened layer with high hardness; An increase in hydrogen content can also form a brittle layer. The hard and brittle surface layer generated by gas absorption can reach a depth of 0.1-0.15 mm, with a hardening degree of 20% -30%. Titanium has a high chemical affinity and is prone to adhesion with friction surfaces.

⑥ Low thermal conductivity and elasticity

The thermal conductivity of titanium, λ=15.24W/(m.K), is about 1/4 that of nickel, 1/5 that of iron, and 1/14 that of aluminum. However, the thermal conductivity of various titanium alloys is about 50% lower than that of titanium. The elastic modulus of titanium alloy is about half of that of steel, so it has poor rigidity and is prone to deformation. It is not suitable for making slender rods and thin-walled parts. During cutting, the springback of the machined surface is large, about 2-3 times that of stainless steel, causing severe friction, adhesion, and bonding wear on the back surface of the tool.

Source: light alloy National Engineering Research Center application base, network arrangement