Of 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 the lowest strength is aluminum alloy.
However, 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 high specific strength, but titanium alloy is expensive and has poor processing performance. Therefore, magnesium alloy is often used in structural parts that need to consider weight and strength comprehensively. This article will comprehensively analyze the characteristics of these alloy materials:
Magnesium and magnesium alloys
1. Magnesium (Mg)
Magnesium has a low density and is easy to burn, which is determined by its physical and chemical properties. The density of magnesium metal at 20℃ is 1.738g/cm3, and the density of liquid magnesium metal is 1.58g/cm3; under standard atmospheric pressure, the melting point of magnesium metal is (650±1)℃, and the boiling point is 1090℃. When heated in air, magnesium metal begins to burn at 632℃～635℃. Therefore, the preparation and alloy smelting process of magnesium are relatively complicated.
The purity of industrial magnesium can reach 99.9%, but pure magnesium cannot be used as a structural material. The magnesium alloy formed by adding aluminum, zinc, lithium, manganese, zirconium and rare earth elements to pure magnesium has high strength. At present, the most widely used is magnesium-aluminum alloy, followed by magnesium-manganese alloy and magnesium-zinc-zirconium alloy. It is mainly used in aviation, aerospace, transportation, chemical industry, rocket and other industrial sectors.
2. Characteristics of magnesium alloy
Light weight
The specific gravity of magnesium is only 1.8G/CM3, and the specific gravity of aluminum alloy is 2.7G/CM3. Magnesium alloy is 30% lighter than aluminum alloy and 80% lighter than steel. Therefore, magnesium alloy has become an ideal material for parts manufacturing in automobiles and portable electronic products.
Strength
Magnesium alloy has an excellent strength/weight ratio among engineering materials such as metals and plastics. Yield strength is 160MPa and tensile strength is 240MPa.
Die-casting
Under good structural conditions, magnesium alloy allows the minimum wall thickness of the casting to reach 0.6mm, which is impossible for plastics at the same strength. The die-casting performance of aluminum alloy must be above 1.2-1.5mm to be comparable to that of magnesium alloy. Magnesium alloy is easier to die-cast and is suitable for large-scale die-casting production (the production speed can reach 1.5 times that of aluminum). In addition, the wear of magnesium alloy molds is also lower than that of aluminum. The main reason is the high viscosity of aluminum.
Shock absorption
Magnesium has excellent hysteresis and shock absorption properties, which can absorb vibration and noise. It can be used as a device casing to reduce noise transmission, prevent impact and prevent dent damage. It is good as a backplane for LCD or LED.
Rigidity
The rigidity of magnesium is twice that of aluminum and higher than most plastics. Magnesium has good stress resistance.
High electromagnetic interference barrier
Magnesium alloys have good electromagnetic wave blocking function and are suitable for the production of electronic products.
Good cutting performance
Magnesium has better cutting performance than aluminum and zinc, making magnesium a metal material that is easier to cut. The specific heat capacity of magnesium alloys is small, and the alloy liquid cools quickly. Magnesium alloys have low affinity with mold steel and are not easy to adhere to the mold.
3. Advantages of magnesium alloy materials
Light weight
Magnesium alloy has the lightest specific gravity among all structural alloys. Its specific gravity is 68% of aluminum alloy, 27% of zinc alloy, and 23% of steel. In addition to being used as the shell and internal structural parts of 3C products, it is also an excellent material for parts such as automobiles and aircraft.
High specific strength and specific stiffness [From Wikipedia]
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 far higher than engineering plastics, which is 10 times that of general plastics.
Good vibration resistance
Under the same load, the vibration reduction is 100 times that of aluminum and 300-500 times that of titanium alloy.
Good electromagnetic shielding
The shell of 3C products (mobile phones and computers) must be able to provide excellent anti-electromagnetic protection, and the magnesium alloy shell can completely absorb electromagnetic interference with a frequency exceeding 100db.
Good heat dissipation
The thermal conductivity of general metals is hundreds of times that of plastics. 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. The specific heat is close to that of water, which is the highest among commonly used alloys.
Good texture
The appearance and touch texture of magnesium alloys are excellent, making the product more luxurious.
Good recyclability
As long as it costs 4% of the price of new materials, magnesium alloy products and waste can be recycled.
Stable resource supply
The reserves of magnesium in the earth’s crust rank eighth, and most of the magnesium raw materials are extracted from seawater, so its resources are stable and sufficient.
4. Advantages of magnesium alloy pressure casting
High productivity, high precision, good surface quality, fine casting grains, and can be die-cast thin-walled and complex structure products.
Aluminum alloy
1. Aluminum alloy
A general term for alloys based on aluminum. The main alloying elements are copper, silicon, magnesium, zinc, and manganese, and the secondary alloying elements are nickel, iron, titanium, chromium, lithium, etc.
Aluminum alloys have low density, but high specific strength, close to or exceeding high-quality steel, good plasticity, and can be processed into various profiles. They have excellent electrical conductivity, thermal conductivity, and corrosion resistance. They are widely used in industry, and their usage is second only to steel.
2. Classification of aluminum alloys
Aluminum alloys are divided into two categories: cast aluminum alloys, which are used in the cast state; deformed aluminum alloys, which can withstand pressure processing and have higher mechanical properties than cast state. Aluminum alloys can be processed into various forms and specifications. Mainly used in the manufacture of aviation equipment, daily necessities, doors and windows for construction, etc.
3. Aluminum alloy processing methods
Aluminum alloys can be divided into deformed aluminum alloys and cast aluminum alloys according to the processing method. Deformed aluminum alloys are divided into non-heat-treatable and heat-treatable aluminum alloys. Non-heat-treatable aluminum alloys cannot improve mechanical properties through heat treatment, and can only be strengthened through cold working deformation. They mainly include high-purity aluminum, industrial high-purity aluminum, industrial pure aluminum, and rust-proof aluminum. Heat-treatable aluminum alloys can improve mechanical properties through heat treatment methods such as quenching and aging. They can be divided into hard aluminum, forged aluminum, super-hard aluminum, and special aluminum alloys.
Aluminum alloys can be heat-treated to obtain good mechanical properties, physical properties, and corrosion resistance. Cast aluminum alloys can be divided into aluminum-silicon alloys, aluminum-copper alloys, aluminum-magnesium alloys, and aluminum-zinc alloys according to their chemical composition.
Zinc alloy
1. Characteristics of zinc alloy
The grade of zinc-based alloy materials commonly used for electroplating is ZnAl 4-1, composition (%): Al 3.5～4. 9, Cu 0.75～1.25, Mg 0.03～0.08, and the balance is Zn.
It has a high specific gravity and good casting performance. It can die-cast complex and thin-walled precision parts with smooth casting surface.
It can be surface treated, electroplated, sprayed, and painted. It does not absorb iron during melting and die-casting, does not corrode the die, and does not stick to the mold. It has good mechanical properties and wear resistance at room temperature. It has a low melting point and melts at 385℃, making it easy to die-cast.
2. Matters to be noted during use
Poor corrosion resistance
When the impurity elements lead, cadmium, and tin in the alloy composition exceed the standard, the casting will age and deform, which is manifested as volume expansion, and the mechanical properties, especially plasticity, will decrease significantly, and even break over time. Lead, tin, and cadmium have very low solubility in zinc alloys, so they are concentrated at the grain boundaries and become cathodes, and aluminum-rich solid solutions become anodes. In the presence of water vapor (electrolyte), intergranular electrochemical corrosion is promoted. Die castings age due to intergranular corrosion.
Aging effect
The structure of zinc alloy is mainly composed of zinc-rich solid solution containing Al and Cu and Al-rich solid solution containing Zn, and their solubility decreases with the decrease of temperature. However, due to the extremely fast solidification speed of die castings, the solubility of solid solution is greatly saturated at room temperature. After a certain period of time, this supersaturation phenomenon will gradually be relieved, and the shape and size of the casting will change slightly.
Zinc alloy die castings should not be used in high temperature and low temperature (below 0℃) working environment. Zinc alloy has good mechanical properties at room temperature. However, the tensile strength at high temperature and the impact performance at low temperature are significantly reduced.
3. Comparison of zinc alloy and magnesium alloy
Composition difference
Magnesium alloy is mainly composed of magnesium, and usually adds aluminum, zinc, manganese and other elements. Zinc alloy is mainly composed of zinc, and usually adds aluminum, copper, magnesium and other elements. Therefore, the composition of the two alloys is significantly different, which also leads to their different performance characteristics.
Differences in mechanical properties
In terms of mechanical properties, magnesium alloys have a low density, high strength, good rigidity, strong impact resistance, and good corrosion resistance, so they are widely used in aerospace, automobiles, electronic products and other fields. Zinc alloys have a high density and relatively poor mechanical properties, but have good casting and surface treatment properties, and are often used in molds, die castings, hardware products and other fields.
Differences in corrosion resistance
Due to different compositions, the corrosion resistance of magnesium alloys and zinc alloys is also different. Magnesium alloys are easy to oxidize and corrode in the atmosphere, but some magnesium alloys can greatly improve their corrosion resistance after special treatment. Zinc alloys are prone to corrosion in a humid environment, but their corrosion resistance can be improved by appropriate surface treatment methods.
Other differences
In addition to the above main differences, there are other differences between magnesium alloys and zinc alloys. For example: magnesium alloys have strong combustion performance and are easy to ignite; zinc alloys have relatively poor combustion performance and are not easy to burn even at high temperatures. In addition, due to the active electrochemical properties of magnesium alloys, they are prone to self-corrosion; although zinc alloys are not easy to self-corrode, their electrochemical properties are relatively poor.
Therefore, although magnesium alloy and zinc alloy are both common metal alloys, there are obvious differences in their composition, mechanical properties, corrosion resistance and other aspects. Therefore, in specific applications, it is necessary to select according to different needs and use environments.
Titanium alloy
Titanium alloy is an alloy composed of titanium and other elements. Titanium has two isomorphous forms: α titanium with a close-packed hexagonal structure below 882°C and β titanium with a body-centered cubic structure above 882°C.
Alloy elements can be divided into three categories according to their effect on phase transition temperature:
Elements that stabilize the α phase and increase the phase transition temperature are α-stabilizing elements, including aluminum, carbon, oxygen and nitrogen. Among them, aluminum is the main alloying element of titanium alloy, which has a significant effect on improving the room temperature and high temperature strength of the alloy, reducing the specific gravity and increasing the elastic modulus.
Elements that stabilize the β phase and reduce the phase transition temperature are β-stabilizing elements, which can be divided into two types: isomorphous and eutectoid. The former includes molybdenum, niobium, vanadium, etc.; the latter includes chromium, manganese, copper, iron, silicon, etc.
Elements that have little effect on the phase transition temperature are neutral elements, such as zirconium and tin.
1. Characteristics of titanium alloys
Titanium is a new type of metal. The performance of titanium is related to the impurity content of carbon, nitrogen, hydrogen, oxygen, etc. The impurity content of the purest titanium iodide does not exceed 0.1%, but its strength is low and its plasticity is high.
High strength
The density of titanium alloys 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. Some high-strength titanium alloys exceed the strength of many alloy structural steels. Therefore, the specific strength (strength/density) of titanium alloys is much greater than that of other metal structural materials, and parts with high unit strength, good rigidity and light weight can be produced. Titanium alloys are used in aircraft engine components, skeletons, skins, fasteners and landing gear.
High thermal strength
The operating temperature is several hundred degrees higher than that of aluminum alloy. It can still maintain the required strength at medium temperature and can work for a long time at 450-500℃. These two types of titanium alloys still have high specific strength in the range of 150℃-500℃, while the specific strength of aluminum alloy decreases significantly at 150℃. The working temperature of titanium alloy can reach 500℃, while that of aluminum alloy is below 200℃.
Good corrosion resistance
Titanium alloy works in humid atmosphere and seawater medium, and its corrosion resistance is far better than that of stainless steel; it has particularly strong resistance to pitting, acid corrosion, and stress corrosion; it has excellent corrosion resistance to alkali, chloride, chlorine organic substances, nitric acid, sulfuric acid, etc. However, titanium has poor corrosion resistance to reducing oxygen and chromium salt media.
Good low-temperature performance
Titanium alloy can still maintain its mechanical properties at low and ultra-low temperatures. Titanium alloys with good low-temperature performance and extremely low interstitial elements, such as TA7, can still maintain a certain plasticity at -253℃. Therefore, titanium alloy is also an important low-temperature structural material.
High chemical activity
Titanium has high chemical activity and reacts strongly with O, N, titanium alloy products, CO, CO2, water vapor, ammonia, etc. in the atmosphere. When the carbon content is greater than 0.2%, hard TiC will be formed in the titanium alloy; when the temperature is high, it will also form a hard TiN surface layer when it reacts with N; above 600°C, titanium absorbs oxygen to form a hardened layer with high hardness; when the hydrogen content rises, a brittle layer will also be formed. The depth of the hard and brittle surface layer produced by absorbing gas can reach 0.1-0.15 mm, and the degree of hardening is 20%-30%. Titanium also has high chemical affinity and is prone to adhesion with the friction surface.
Low thermal conductivity elasticity
The thermal conductivity of titanium, λ=15.24W/(m.K), is about 1/4 of nickel, 1/5 of iron, and 1/14 of aluminum, while the thermal conductivity of various titanium alloys is about 50% lower than that of titanium. The elastic modulus of titanium alloy is about 1/2 of that of steel, so it has poor rigidity and is easy to deform. It is not suitable for making slender rods and thin-walled parts. The rebound of the machined surface during cutting is large, about 2 to 3 times that of stainless steel, causing severe friction, adhesion, and bonding wear on the back face of the tool.
2. Comparison between titanium alloy and magnesium alloy
Density comparison
Both titanium alloy and magnesium alloy are light metal materials, much lighter than ordinary steel materials. The density of titanium alloy is about 4.5 g/cm3, while the density of magnesium alloy is only 1.7 g/cm3, so in general, magnesium alloy is lighter than titanium alloy.
Strength comparison
Titanium alloy and magnesium alloy also differ in strength. Titanium alloy has high strength and excellent mechanical properties, and can withstand high temperature and high-intensity stress. Magnesium alloy is relatively soft, has lower strength and hardness, but can also perform well under certain conditions. Therefore, in specific applications, different materials need to be selected according to specific requirements.
Corrosion resistance
Both titanium alloys and magnesium alloys have good corrosion resistance, but magnesium alloys are relatively more corrosive, especially in humid environments, and are prone to corrosion and deformation. Titanium alloys have more excellent corrosion resistance, especially in marine environments, so they are often used in the manufacture of marine engineering equipment.
In general, titanium alloys and magnesium alloys are both excellent light metal materials and are widely used in different fields. Titanium alloys have a relatively large density, but higher strength and better corrosion resistance, and are suitable for manufacturing occasions that require high strength and corrosion resistance. Magnesium alloys are relatively light, but have lower strength, and are usually suitable for manufacturing parts and appliances that require lightweight and softness.
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