Cast aluminum alloy is a kind of aluminum matrix, by adding other alloying elements made of materials, has a series of excellent properties and a wide range of uses.
The properties of cast aluminum alloy mainly include:
Low density and high strength. The density of cast aluminum alloy is usually between 2.63 and 2.85g/cm³, with high strength and specific strength, which can significantly reduce the weight of parts and components and improve the use efficiency.
Good casting performance. Cast aluminum alloy has good fluidity and shrinkage, can be made into complex shape parts, do not need huge additional equipment, with metal saving, reduce costs, reduce working hours and other advantages.
Good corrosion resistance. Cast aluminum alloy in air, water, acid, alkali and other environments can maintain the brightness and finish of the surface, with good corrosion resistance.
Good heat resistance. Compared with cast iron alloys, cast aluminum alloys have a higher melting point and thermal stability, which can maintain excellent performance in high temperature environments.
Good electrical and thermal conductivity. Aluminum alloy has good electrical and thermal conductivity properties, suitable for parts that need good thermal conductivity, such as cylinder heads and pistons of internal combustion engines.
Good processability. Aluminum alloy is easy to process and has excellent plasticity and machinability.
Classification of cast Aluminum alloys
Modern cast aluminum alloy can be divided into 4 series according to the main added elements, namely: aluminum-silicon series, aluminum-copper series, aluminum-magnesium series and aluminum-zinc series. For these 4 series, each country has the corresponding alloy and alloy grade mark. China uses ZL+3 digit marking method, the first digit indicates the alloy system, where: 1 indicates the aluminum-silicon alloy system, 2 indicates the aluminum-copper alloy system, 3 indicates the aluminum-magnesium alloy system, 4 indicates the aluminum-zinc alloy system, the second and three digits indicate the alloy serial number. For example ZL101,ZL201, ZL301,ZL401
Aluminum-silicon alloy
Usually the silicon content is 4% to 13%, also known as "silicon aluminum Ming" alloy. The casting performance is the best, the crack tendency is very small, the shrinkage rate is low, there is a good corrosion resistance and air tightness and enough mechanical properties and welding properties. Although the application of this series of alloy in the industry is later than that of aluminum-copper alloy, it was found in 1920 that after metamorphic treatment, the structure and properties of this series of alloy were improved, and the scope of use was expanded, accounting for almost 50% of the cast aluminum alloy in the amount. Al-si alloy can be divided into eutectic type, hypoeutectic type, hypereutectic type and complex eutectic alloy with addition of copper, magnesium and manganese. ZL102 alloy is a typical binary eutectic alloy with eutectic temperature of 577℃ and eutectic composition of 12.6%Si. At eutectic temperature, 1.6%Si is dissolved in α solid solution, and about 0.05%Si is dissolved at room temperature. The β phase is a solid solution of aluminum dissolved in silicon, and its solubility is very small, so the eutectic structure is composed of α+Si two phases. In addition to α and silicon, there are θ (CuAl2), W (AlxMg5Si4) and other phases in the structure of multicomponent alloys (see the phase of aluminum alloys). Aluminum-silicon alloys containing copper can be strengthened by heat treatment, but the corrosion resistance is poor. The shape of the silicon phase in the alloy has a significant influence on the strength and plasticity. Through the modification treatment (adding sodium or antimony in the melt), the silicon phase is spheroidized, and the microstructure and properties of the alloy are improved. The coarse primary silicon in hypereutectic alloys is harmful to mechanical properties and machinability. Phosphorus is often added to form AlP compounds to refine the primary silicon and reduce its harmful effects.
Aluminum-copper alloy
It is the earliest industrial cast aluminum alloy. The alloys have high strength and thermal stability, but poor castability and corrosion resistance. The copper content is generally lower than the solubility limit of copper in aluminum (5.85%), there is no eutectic in the equilibrium structure, and a small amount of eutectic may appear under non-equilibrium conditions. After solution treatment, the solid solution can be supersaturated and the aging strengthening effect can be obtained. The addition of manganese and titanium to the alloy can refine the grain, strengthen and improve the corrosion resistance.
Aluminum-magnesium alloy
The alloy has high strength, best corrosion resistance, low density and good air tightness. Aluminum magnesium binary casting alloy, the magnesium content is as high as 11.5%, and the magnesium content in the multi-component alloy is generally about 5%. The microstructure of the alloy is α+β (Mg5Al8) phase, and the strengthening effect of heat treatment is not obvious, mainly for solid solution strengthening. When β (Mg5Al8) phase precipitates in a network along the grain boundary, the corrosion resistance and mechanical properties deteriorate. In order to prevent the precipitation of β (Mg5Al8) phase along the grain boundary, it is mostly used in solid solution state. Adding silicon and manganese to the alloy can improve the fluidity of the alloy.
Aluminum-zinc alloy
The alloy has the characteristics of quenching microstructure in the casting state, and high strength can be obtained without heat treatment, but the density of the alloy is large, and it is not suitable for the production of aircraft parts. The alloy system is made of zinc on the basis of silica-alumin alloy, so it is also called "zinc-silica-alumin" alloy.
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