Differences and Advantages of Powder Metallurgy vs. Die Casting
Manufacturers and other related industries consider numerous factors in choosing the best metal forming process for their metal products or components. They must consider the quality of the product and its associated implications. They also have to ponder on the mechanical properties and the intended applications of the same product. The overall cost or pricing of the product can likewise affect their decision when it comes to choosing the best process for their operations.
Two processes that manufacturers can choose are powder metallurgy and die casting. These processes may share some similarities when it comes to a few things. However, they may also have distinct qualities that make one process more advantageous in specific applications and instances than the other.
Qualities of Powder Metallurgy
Powder metallurgy is a type of metal forming process that is initially conducted by compressing metal powders into a shaped mould. Once the compact is formed, the manufacturer will then subject it to heat that is below their respective melting points through a sintering oven. At this point, all the metal powder will be compressed tightly until the finished metal product is formed. All the steps involved in powder metallurgy avoid the need to conduct any metal removal process, resulting in a decrease in yield losses in manufacturing and overall cost.
What is great about powder metallurgy is that it can easily produce products that are at or close to the intended shape, form, and dimensions. Complex or unique shapes can also be achieved whenever this metal forming process is used. The production of metal parts and components in moderate to high volume is likewise possible with powder metallurgy. And for its product, the manufacturer may expect it to obtain a good surface finish, controlled porosity, enhanced strength and reliability, increased wear resistance, and long service life. Products out of powder metallurgy are also cost-effective.
Qualities of Die Casting
Alternatively, die casting is a metal forming process that subjects molten metal under high pressure and high filling speed into a mould cavity. Alloys that are used for die casting typically have low melting points are made from non-ferrous metals. The molten metal from this process typically comes from a furnace where non-ferrous metals are melted. Consequently, this specific metal is injected into the dies, which can be found in the die casting machine. The die casting machine then cools and solidifies the molten metal component.
Die casting is utilised by manufacturers and other industries due to its ability to quickly produce materials. Mass production of complex shapes with little to no machining requirements is possible with die casting. Products that are processed by die casting can contain enhanced durability, improved stability, and smooth or textured surfaces. These products can even be plated or finished without any complicated surface preparation. Die casting products can also make the assembly simpler as they can easily provide fastening elements like bosses and studs.
Powder Metallurgy vs. Die Casting
The whole process of powder metallurgy tends to bring more advantages compared to the die casting. It can provide more consistent and high-quality products. The products they can produce can also have greater flexibility and higher variability. The cost of conducting powder metallurgy is also cheaper.
The properties of alloys that are processed from sintered aluminium power (SAP) are different compared to other materials. The oxide on these alloys’ surface, which forms during sintering, does not reduce back to the materials. As a result, a huge amount of oxide retains on the surface of these alloys, allowing them to produce high strength, high creep resistance, and high-temperature resistance. This oxide surface also prevents the alloy from obtaining grain growth and dislocation activities at the boundaries.
Creating Sintered Aluminium Powder Products
Naturally formed oxide that retains on the surface of SAP-type products, as well as the elements integrated with them, would determine the overall properties of these products. Unlike some processed materials, increasing the thickness of the oxide film does not provide SAP-type products with more strength. Instead, the increased thickness will only reduce their overall ductility.
SAP-type products can be made by numerous methods. One way to create them is to disperse aluminium oxide into molten aluminium with the help of ultrasonic vibration. Another way to create these products is by blowing reducible oxides into an aluminium melt. The natural oxide that is created out of these methods would usually contain absorbed water, which reacts with the metal to create additional oxide and give off hydrogen. If the processed product has high oxide content, then it will release more hydrogen, which can cause cracking or blistering. As a solution, these products would need to undergo vacuum treatment or high-temperature sintering to prevent the effects of hydrogen.
Sintered Aluminium Powder Product Properties
- Structure: As mentioned, the structure of SAP-type products depends on the fabrication technique and their respective oxide composition. The iron and silicon elements that can be found in the aluminium fragment are usually dispersed in the metal. Both elements can act as starting points for fracture.
- Density: The density of SAP elements falls between 900 to 1,000 kg/m3. However, the density can reach 2,710 to 2,720 kg/m3 when the powders are compacted to 95% or better. Any integration of heavy metals can increase their overall density.
- Thermal Expansion: The thermal expansion coefficient of SAP elements is much lower than pure aluminium. It even falls linearly whenever their oxide composition increases. The thermal conductivity of SAP products cuts down by around 1% for every 1% of oxide presence.
- Electric Resistivity: An unbroken oxide film on the surface of SAP elements would normally result in electric resistivity of as high as 1 Ωm. On the other hand, the resistivity will decrease by 2.9 x 10-8Ωm to 10-8 Ωm when the oxide film is ruptured with high-temperature sintering or extrusion.
- Grain Strength: The grain strength of SAP elements is normally proportional to the area of contact of the particles. After sintering, the ductility is inversely proportional to the oxide content. The size of the grain of a sintered product does not have any effect on this powder, but the coarse grain at high temperatures can increase its strength and ductility.
- Fatigue Strength: The fatigue strength of SAP elements is set at 60 to 70 MPa at 107cycles. The resistance of fatigue may increase by 10 to 20% through the presence of high hydrogen composition. A decrease of fatigue resistance, alternatively, can be seen due to notches and slow strain rates.
- Creep Resistance: SAP elements have extremely high creep resistance compared to all aluminium alloys. The impact strength increases with the rising temperatures, normally within 530 to 570°C. The shear strength also rises with increasing temperature and then declines. The structure or properties of SAP elements will remain unchanged despite numerous years of exposure to high temperatures, making them insensitive to high temperatures.
All these properties of sintered aluminium powder allow them to be used in a lot of useful applications.