Near-eutectic wheel casting alloys
Aluminum cast wheels are mainly produced by the following methods:
- Low pressure die casting
- Gravity die casting
Low pressure die casting
Low pressure casting machine is used, vertically oriented. Molten metal is in a sealed vessel, which is then compressed by a gas (usually air), so that the metal is forced "up" into the mold cavity. way. This process is widely used for the production of automobile wheels..
Fig. 1 – Schematic View of the Low Pressure Die Casting Process [2]
Fig. 2 – Low-pressure permanent mold [3]
Fig. 3 – Aluminium alloy automotive wheels produced by low-pressure casting [3]
Gravity die casting
Gravity die casting is the simplest die-casting process. It enables castings to be produced with only a very modest capital investment, but plenty of hard physical work is required. Good quality castings can be produced if sufficient care is taken to design running and gating systems which minimise surface turbulence in the metal as it flows into the die [1].
Fig. 4 – Schematic View of Gravity Die Casting [2]
Cast aluminum alloys for wheel casting
Chemical composition
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 (Fig. 1). On this basis, especially for manufacturing alloy wheels, alloys have been developed [1]:
- Silumin-Kappa Sr (10,5-11,0 % silicon) and
- Silumin-Beta Sr (9,0-10,5 % silicon).
Table 1 – Chemical composition (all data in wt.-%) [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 %.
Table 2 – Casting characteristics and other properties of castings [1]
Table 3 – Physical properties [1]
Table 4 – Mechanical properties at room temperature +20 °C [1]
Modifying Silumins strontium
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 и 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. Age hardening wheels of Silumin-Kappa alloys generally not recommended due to possible partial embrittlement, which can reduce the fatigue strength of the material.
Table 5 – Heat treatment of aluminium castings [1]
Table 6 – Mechanical properties of gravity die casting samples [1]
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.
Table 7 – Typical process parameters [1]
Sources:
- Aluminium Casting Alloys – Aleris Recycling (German Works) GmbH – 2011
- TALAT 3201
- Aluminum Casting Processes // Aluminum Alloy Castings Properties, Processes, and Applications / J. Gilbert Kaufman, Elwin L. Rooy – 2004
Also: