The density of zinc is 7.133g/cm', the melting point is 4200C, and the boiling point is 9110C. It has a zinc flash crystal lattice with no allotrope. The strength and plasticity of pure zinc are all poor. The electrochemical sequence of zinc is before chromium and iron. The standard electrode potential is a 0.763V. It is easily combined with Cl-'02-plasma, so it is easily corroded in air, various acids and seawater and other media, so pure zinc, The Zn-Al-Cd alloy can be used as a snorkel anode for steel ships or large-scale steel equipment to protect ships and large-scale equipment, and to perform chrome plating or phosphating treatment as components to prevent corrosion.
Addition of alloying elements based on pure zinc Aluminum, copper, and magnesium can form a series of zinc alloys.
Zinc alloy has a certain strength, enough hardness, low melting point, good fluidity, widely used as a die-casting alloy, die castings with high dimensional accuracy, good electroplating performance, widely used in automobile, tractor manufacturing and instrument manufacturing.
Zinc alloy has good wear resistance, and it can also be used for sand casting large and medium-sized bearings, bushings and other wear-resistant parts, compared with babbitt alloy, it has the advantages of low cost, low quality, high hardness, easy molding, easy cutting and so on. Compared with some tin bronzes, the friction coefficient is slightly lower and the mechanical properties are higher. Compared with aluminum bronze wear parts, the affinity with lubricating oil is large, the friction coefficient is small, and the mechanical properties are slightly lower. Zinc alloy stamping dies instead of steel molds can save a lot of man-hours and shorten the cycle time of the molds. It is also possible to manufacture lamps and arts and crafts using zinc alloy shells. Another feature of zinc alloy is that it has vibration-reducing performance and can produce automobile transmissions, fan parts, etc., which can reduce noise. The disadvantages of zinc alloys are: Compared with aluminum alloys, the density is high, the coefficient of thermal expansion is large, and the high temperature strength and room temperature plasticity are all lower, thus limiting its use.
The main alloying elements in the zinc alloy are Al.Cu, Mg, and their effects on the zinc alloy are as follows.
1. Al-Zn binary phase diagram, as shown in Figure 5-4, β.α is a solid solution based on Zn. Al, and the crystallization process of the alloy is as follows.
There is a eutectic transformation at 382°C containing Al 5%: L→β+α contains Al at 22.3% at 275°C. The eutectoid transformation occurs: α→β+α1. When the precipitation in the middle and the Al-containing temperature higher continue to fall, the composition of the moon phase is basically unchanged, and the composition of al is continuously changed. At room temperature, the composition of a, is close to that of pure aluminum. Therefore, under the condition of equilibrium, the Al content is low. In 22.3% of zinc alloys, its structure consists of β+(β+α1) eutectoids. The non-equilibrium structure under the casting conditions does not undergo eutectoid transformation and consists of β+(β+α). The a phase at room temperature is actually a Zn-containing supersaturated solid solution, which gradually decomposes into aluminum-rich over time. a, Phase and zinc-rich f3 phase. In the decomposition process accompanied by volume expansion, the formation of a huge internal stress in the casting, promote intragranular corrosion, plastic significantly reduced, making the alloy brittle, this decomposition process is the natural aging process, often referred to as "aging.
Al is the main alloying element of zinc alloys, and the enhanced phase and a phase appear in the structure, and the strength and plasticity are improved.
2. Cu Zn-Al binary alloy added Cu 'in addition to a small amount of solid dissolved in the month, a phase, but also the formation of electronic compounds CuZn3-based solid solution, Zn-AI-Cu ternary state diagram shown in Figure 14-1 . Further alloying improves strength and hardness, improves fluidity, improves casting performance, and improves corrosion resistance. The disadvantage of adding Cu is to promote the decomposition of phase a, make the casting size unstable, and accelerate the "aging" of the alloy.
3. Mg Mg solid solution in β, a, can reduce the intragranular corrosion, increase the strength, hardness, reduce the eutectoid transformation temperature, inhibit the decomposition of a phase, to prevent the alloy. Ageing,. However, the addition of excess amounts to the formation of intermetallic compounds reduces the plasticity and increases the tendency of hot cracking and cold cracking. Mg forms a MgO film on the liquid surface, which reduces the fluidity.
Arc Shape Magnet,Block Shape Magnet,Disc Shape Magnet,Ring Shape Magnet
YangYi Magnetics Co., Ltd. , http://www.hz-magnets.com