European aluminum-silicon alloy Al Si11 (44000) with a silicon content slightly below the eutectic (from 10,0 to 11,8 %) is widely used for the manufacture of rims by low-pressure casting. On this basis, especially for manufacturing alloy wheels, alloys have been developed:
- Silumin-Kappa Sr (10,5-11,0 % silicon) and
- Silumin-Beta Sr (9,0-10,5 % silicon).
Chemical composition of the aluminum alloy is shown in Figure 1.
Casting hypoeutectic silumin
These aluminum casting alloys:
- It has good fluidity,
- high plasticity and
- good corrosion resistance.
Cast alloy Silumin-Kappa Sr has an optimum content of silicon 10,5 to 11,0 %. In the alloy Silumin-Beta Sr interval silicon content is from 9,0 to 10,5 %.
Usually, these alloys are modified strontium at the stage of pig production, and therefore they do not require this modification directly in the foundry industry. strontium additives in these alloys ranges from 0,020 to 0,030 %.
Modification of eutectic silicon, that is, the formation of the modified microstructure necessary to improve the ductility of the cast structure wheels, which is produced from these alloys. The level of gland and other impurities greatly affects the plasticity of the cast structure - elongation performance.
Effect of magnesium on silumins
If necessary, these alloys can be cast magnesium content between 0,05 and 0,45 %. With an increase in the magnesium content of the alloy strength is increased slightly, and ductility also slightly reduced. On the other hand, magnesium additives to improve the machinability of these alloys cutting, as it promotes the formation of the chip and its removal when machining wheels.
This gives the wheel disks more attractive appearance. Moreover, Mg increases the resistance to corrosion of disks, but decreases the adhesion of protective paint coatings to the surface of the wheel rim.
Heat treatment Silumins Beta and Kappa
Only some of Silumin-Beta-type alloys are thermally reinforcing. thermal hardening wheels of Silumin-Kappa alloys generally not recommended due to possible partial embrittlement, which can reduce the fatigue strength of the material.
Silumin Al Si7Mg for rims
Thermally hardened aluminum rims are made of aluminum alloy Al Si7Mg (commercial name - Pantal 7). solidification of this alloy type - hypoeutectic. During solidification occurs transition from liquid to pasty. Upon subsequent solidification aluminum dendrites grow into the liquid melt. They form an interwoven network, and the cavity therebetween filled with a eutectic AlSi vysokotekuchey, which then hardens. If the make-up of these "voids" for whatever reason is not sufficient, then there are defects such as microporosity. solidification range is about 35-40 ° C.
Purification melt silumin
Purification melt alloys of this type is carried out by blowing only inert gases or by vacuum treatment. Processing materials melt, containing chlorine, not allowed, as this occurs leaching strontium melt.