Zinc alloy
01. Characteristics of zinc alloy
The grade of zinc-based alloy material usually 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.
①The proportion is large
② Good casting performance can die-cast precision parts with complex shapes and thin walls, and the surface of the castings is smooth
③ Surface treatment available: electroplating, spraying, painting
④ No iron absorption during melting and die-casting, no corrosion of the pressing type, no sticking to the mold
⑤Good mechanical properties and wear resistance at room temperature
⑥ Low melting point, melting at 385°C, easy to die-cast
02. Problems to be noticed during use
① Poor corrosion resistance.
When the impurity elements lead, cadmium, and tin in the alloy composition exceed the standard, the casting will be aged and deformed, manifested as volume expansion, mechanical properties, especially plasticity, will decrease significantly, and even crack after a long time. The solubility of lead, tin, and cadmium in zinc alloy is very small, so they concentrate on the grain boundary and become the cathode, and the aluminum-rich solid solution becomes the anode, which promotes intergranular electrochemical corrosion in the presence of water vapor (electrolyte). Die castings age due to intergranular corrosion.
② 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 the die casting, the solubility of the 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.
③ Zinc alloy die castings are not suitable for use in high temperature and low temperature (below 0°C) working environments.
Zinc alloys have good mechanical properties at room temperature. However, the tensile strength at high temperature and the impact performance at low temperature are significantly decreased.
03. Comparison of zinc alloy and magnesium alloy
①Ingredient difference
Magnesium alloys use magnesium as the main component, and usually add elements such as aluminum, zinc, and manganese. Zinc alloys use zinc as the main component, and usually add elements such as aluminum, copper, and magnesium. Therefore, the composition of the two alloys is significantly different, which also leads to their different performance characteristics.
② Difference in mechanical properties
In terms of mechanical properties, magnesium alloys have 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 higher density and relatively poor mechanical properties, but they have good casting properties and surface treatment properties, and are often used in molds, die-casting parts, hardware products and other fields.
③ Differences in corrosion resistance
Due to the difference in composition, the corrosion resistance of magnesium alloy and zinc alloy is also different. Magnesium alloys are easy to oxidize and corrode in the atmospheric environment, but some magnesium alloys can greatly improve their corrosion resistance after special treatment. Zinc alloys are prone to corrosion in wet environments, but their corrosion resistance can be improved by proper surface treatment.
④Other differences
Apart from the main differences above, there are some other differences between magnesium alloys and zinc alloys. For example: magnesium alloy has strong combustion performance and is easy to ignite; zinc alloy has relatively poor combustion performance and is not easy to burn even at high temperatures. In addition, due to the active electrochemical properties of magnesium alloys, it is prone to self-corrosion; although zinc alloys are not prone to self-corrosion, their electrochemical properties are relatively poor.
In summary, although magnesium alloys and zinc alloys are common metal alloys, there are obvious differences in their composition, mechanical properties, and corrosion resistance. Therefore, in specific applications, it is necessary to choose according to different needs and usage environments.
Titanium alloy
Titanium alloy is an alloy composed of titanium as the base and other elements. Titanium has two kinds of allotropic crystals: below 882°C is close-packed hexagonal structure α-titanium, and above 882°C is body-centered cubic β-titanium.
Alloying elements can be divided into three groups according to their effect on the phase transition temperature:
① The elements that stabilize the α phase and increase the phase transition temperature are α stable elements, such as aluminum, carbon, oxygen and nitrogen. Among them, aluminum is the main alloying element of titanium alloy, which has obvious effects on improving the strength of the alloy at room temperature and high temperature, reducing the specific gravity and increasing the modulus of elasticity.
②The elements that stabilize the β-phase and lower the phase transition temperature are β-stable elements, which can be divided into two types: isocrystal and eutectoid. The former includes molybdenum, niobium, vanadium, etc.; the latter includes chromium, manganese, copper, iron, silicon, etc.
③ The elements that have little effect on the phase transition temperature are neutral elements, such as zirconium and tin.
01. Characteristics of titanium alloy
Titanium is a new type of metal. The performance of titanium is related to the content of impurities such as carbon, nitrogen, hydrogen, and oxygen. The purest titanium iodide has an impurity content of no more than 0.1%, but its strength is low and its plasticity is high.
①High strength
The density of titanium alloy is generally about 4.51g/cubic centimeter, 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. Therefore, the specific strength (strength/density) of titanium alloy 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.
②High heat intensity
The service temperature is several hundred degrees higher than that of aluminum alloy, and it can still maintain the required strength at medium temperature, and can work for a long time at a temperature of 450-500°C. These two types of titanium alloys still have high strength in the range of 150°C-500°C. Specific strength, while the specific strength of aluminum alloy decreases significantly at 150 °C. The working temperature of titanium alloy can reach 500°C, while that of aluminum alloy is below 200°C.
③Good corrosion resistance
Titanium alloy works in humid atmosphere and seawater medium, and its corrosion resistance is far superior to that of stainless steel; it has particularly strong resistance to pitting corrosion, acid corrosion, and stress corrosion; it is resistant to alkali, chloride, chlorine, organic substances, nitric acid, and sulfuric acid. etc. have excellent corrosion resistance. However, titanium has poor corrosion resistance to media with reducing oxygen and chromium salts.
④Good performance at low temperature
Titanium alloys can still maintain their mechanical properties at low and ultra-low temperatures. Titanium alloys with good low temperature performance and extremely low interstitial elements, such as GR6, can maintain certain plasticity at -253°C. Therefore, titanium alloy is also an important low-temperature structural material.
⑤ High chemical activity
Titanium has high chemical activity, and has strong chemical reactions 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, the TiN hard surface layer will be formed when it interacts with N; when the temperature is above 600 ° C, titanium absorbs oxygen to form a hardened layer with high hardness ; When the hydrogen content rises, an embrittlement 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%. The chemical affinity of titanium is also large, and it is easy to cause adhesion with the friction surface.
⑥Small thermal conductivity
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 modulus of elasticity 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. times, resulting in severe friction, adhesion, and bond wear on the flank of the tool.
02. Comparison of titanium alloy and magnesium alloy
①Comparison of density
Both titanium alloy and magnesium alloy are light metal materials, which are much lighter than ordinary steel materials. Titanium alloys have a density of about 4.5 g/cm3, while magnesium alloys have a density of only 1.7 g/cm3, so magnesium alloys are generally lighter than titanium alloys.
②Strength comparison
Titanium and magnesium alloys also differ in strength. Titanium alloy has high strength and excellent mechanical properties, and can withstand high temperature and high-intensity stress. Magnesium alloys are softer and have lower strength and hardness, but they can also perform well under certain conditions. Therefore, different materials need to be selected according to specific requirements in specific applications.
③Corrosion resistance
Both titanium alloy and magnesium alloy have good corrosion resistance, but magnesium alloy is still relatively strong in corrosion, especially in a humid environment, it is easy to corrode and deform. Titanium alloys have better corrosion resistance, especially in marine environments, so they are often used in the manufacture of marine equipment.
In general, titanium alloys and magnesium alloys are excellent light metal materials, which are widely used in different fields. The density of titanium alloy is relatively high, but its strength is higher, and its corrosion resistance is better. It is suitable for the occasions that require high strength and corrosion resistance. Magnesium alloys are relatively light, but low in strength, and are usually suitable for the manufacture of parts and appliances that require lightweight and softness.
