Investment casting is a versatile metalworking process used to shape pipe fittings, automotive parts, marine hardware and food machinery. There are a wide variety of metals that can be used for investment casting, and they have different properties that make them suitable for a variety of applications.
Investment casting materials include ferrous and non-ferrous metals. Of the various ferrous metals, ductile iron, carbon and alloy steels, and selected grades of stainless steel are used the most. Non-ferrous metals such as copper alloys, magnesium and aluminum can also be used, with aluminum being the most popular.
metals for investment casting
aluminum alloy
Aluminum alloys for investment casting have a density of 2.7 g/cm3 or slightly higher. Types of aluminum parts that are investment cast include aircraft and engine parts. Aluminum alloys A-356, A-357, C-355 and F-357 containing silicon, magnesium, iron and zinc are used the most. Components made of aluminum are corrosion resistant, weldable, and some have extraordinary strength.
Stainless steel
Stainless steel is a ferrous metal that contains chromium for added protection against stains and corrosion. There are several grades of stainless steel, each with beneficial properties. Variations in stainless steel are due to the chemical composition of its alloys. Stainless steel is an ideal metal for parts exposed to high temperatures or liquid environments.
The main stainless steel grades used for investment casting are the 300 and 400 series. Austenitic 300 series stainless steels have excellent corrosion resistance but do not gain strength through heat treatment. Martensitic 400 series stainless steels have excellent strength and machinability and can be hardened by quenching and tempering to increase their strength.
Carbon steel
Carbon steel is one of the better choices for investment casting products because it can operate under high pressure, is wear-resistant, and has excellent strength, toughness, and hardenability. The properties of carbon steel depend on the amount of carbon it contains, which increases its hardness and strength during heat treatment.
Medium and low carbon steels are most commonly used in investment casting. Medium carbon steel has ductility, strength and wear resistance and can be hardened and tempered by heat treatment. Mild steel is easy to form, but cannot be strengthened by heat treatment.
nickel alloy
Nickel alloy has high strength, heat resistance, corrosion resistance and wear resistance. They can be welded and fabricated, and are resistant to cracking or stress corrosion. The primary use of nickel alloy investment castings is in conditions with high temperatures and corrosive elements.
The popularity of nickel alloy investment castings is due to their tight tolerances and exceptionally smooth surface finish, as well as their ability to be machined into complex and intricate shapes. Among the various investment casting metals, nickel alloys are a cost-effective solution.
copper alloy
Copper alloys are corrosion resistant, thermally conductive and tough. They are used in investment casting due to their ease of casting. Copper alloys are machinable and have excellent mechanical properties and friction and wear resistance.
Copper alloy types for investment casting include the series C-84500, C-85800, C-86000, C-87000, C-90000, and C-95000. The wide range of alloys provides enough options to select the correct alloy for any application.
cobalt alloy
Cobalt alloys have high strength and heat and wear resistance. They are naturally resistant to oxidation and have an extremely high melting point, making them ideal for corrosive and chemically charged environments. Cobalt alloys are resistant to creep and thermal fatigue in high temperature applications.
Various cobalt alloys contain combinations of chromium, nickel, tungsten and molybdenum; this changes its properties and resistance type. Cobalt alloys for investment casting are No. 6, No. 21, No. 25, No. 31 and No. 93.
magnesium
For many years, casting magnesium using investment casting has been difficult due to the reaction of the molten magnesium with the silica mold shell. More recently, an inhibitor was introduced to allow magnesium to be used in investment casting.
Magnesium is lightweight and has an excellent strength-to-weight ratio. It is versatile and available in a variety of alloys including AZ91D and AM60B, as well as AZ81, AM50A, AM20, AE42 and AS41B for creep resistant and high temperature applications.