What is alloy casting and how is it different from conventional casting?
Alloy casting is the process of melting an alloy and pouring it into a mold to get the desired part. Generally, alloy casting involves the melting of alloys, but it can also be performed by melting and mixing different metals to form the alloy during casting, and then solidifying it.
This article discusses alloy casting in detail by going through its process, benefits, and types of alloys suitable for casting.
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What is Alloy Casting? Explained
Alloy casting is the process of melting an alloy and allowing it to solidify in the mold cavity, taking the desired shape.
This process either uses pre-alloyed metals or involves the mixing of different alloys during the melting process and then solidifying it, resulting in an alloy casting.
The addition of alloying metals is generally performed to alter the properties of the metal.
Some of the common properties altered by adding alloying metals include corrosion resistance, machinability, weldability, strength, cost, etc.
How is Alloy Casting Done?
Alloy casting involves melting alloys and following the conventional gravity die-casting process to get the desired alloy workpiece.
Mainly you need metal melting tools such as a furnace, ladle to pour molten alloy, work gloves, eye protection glasses, mold, etc.
Ferrous alloys are iron-based alloys and provide flexibility, strength, and toughness.
Nonferrous alloys are those that contain a high concentration of metals such as aluminum, nickel, copper, cobalt, tin, and zinc.
If you are looking for lightweight, high-strength, high corrosion-resistant materials then nonferrous alloys are the best choice.
When performing alloy casting, it is important to consider that different metals have different melting points.
Therefore, it is important to gradually heat the workpiece to melt the metals in sequential order.
Similarly, when adding different metals to form an alloy for casting, it is advised to start by melting the metal that has the lowest melting point, and then add the metals having a comparatively higher melting point.
This is done because adding a low melting point metal in a hot metal pool (above its melting point) can result in a flash.
For example, when alloying copper and aluminum (aluminum bronze), if you add aluminum to a copper melt, it will result in a minor explosion in the form of a flash, splashing the molten metal.
This is because the melting temperature of copper is around 1,984°F while that of aluminum is around 1,221°F, and adding aluminum to molten copper results in instant vaporization of aluminum, causing a flash.
As a result, it is always advised to melt aluminum first, followed by the addition of copper and gradually heating to avoid flash.
To increase the quality of alloy casting, flux can be added during metal melting.
It acts as a purifying agent, preventing the formation of undesirable impurities/slag. The most common flux material is borax.
After melting the alloy, the hot melt is poured into a die and allowed to solidify in it, producing the desired casting.
The process of casting and molding follows a similar workflow, the difference lies in the workpiece material.
While casting is used for metal workpieces, molding is concerned with plastic materials, such as injection molding.
4 Benefits of Alloy Casting
Depending upon the type of alloy and the amount of alloying elements added to the metal, alloy casting provides various advantages over traditional castings.
Adding alloying elements often provides the opportunity to enhance the machinability of metals.
For example, pure copper is difficult to machine due to its high ductility, and adding alloying elements such as zinc, tin, silicon, etc. can improve the machinability of copper casting.
Making it suitable for further machining to achieve the desired surface finish and dimensional accuracy.
Alloying elements such as carbon, copper, manganese, nickel, chromium, and molybdenum increase the strength of the metal.
Therefore, adding these alloying elements to the casting results in high strength of the final casting product.
Improved Corrosion Resistance
Alloying elements such as Molybdenum, Chromium, etc., enhance the corrosion resistance of the metal, making it suitable for casting products that are to be subjected to corrosive conditions.
The fluidity of the molten metal plays an important role in determining the quality of the casting.
After pouring the metal into the mold, it flows into the die cavity, taking up the shape of the die.
However, poor fluidity results in casting defects where the metal solidifies without completely filling the mold.
Therefore, adding alloying substances that enhance the fluidity will enhance the flow of molten metal inside the die, making it possible to produce intricate casting with no or minimal defects.
Types of Alloys Suitable for Casting
Ferrous alloys are those alloys that have iron as their primary constituent, while other metals are added to specifically alter their properties, making them suitable for different applications.
It is an iron alloy containing carbon and other elements such as aluminum, titanium, silicon, or manganese.
The hardness and strength of carbon steel increase with increasing carbon content, and based on your requirement, you can select the right carbon content for your application.
Generally, low-carbon steel consists of around 0.25% carbon and is suitable for low-strength applications like brackets, links, and casing.
Medium carbon steel with up to 0.55% carbon can be used for products such as levers and machine parts that require strong ductility, shock, and fatigue strength.
High-carbon steel (up to 1% carbon) can be used for components requiring high strength, such as heavy-duty cranks or pins.
Stainless steel is another ferrous alloy that contains carbon and around 11% chromium.
It is best suited for food processing, medical equipment, and aviation accessories, due to its high resistance to corrosion and stains.
Manganese Alloy Steels
This alloy is commonly useful for applications that require excellent wear resistance such as construction and mining equipment, railroad equipment, crushing equipment, etc.
Adding manganese to steel enhances its abrasion resistance, thereby minimizing the wear, even when subjected to extreme conditions.
Unlike ferrous alloys, these alloys have a non-ferrous base metal.
Copper, tin, zinc, aluminum, nickel, etc., are some common non-ferrous and non-magnetic metals.
Copper-Zinc Alloy (Brass)
Brass is a low-cost alloy that has good castability and machinability, as well as excellent corrosion- and wear resistance.
If your DIY project requires electrical fittings, locks, musical instruments, or decorative items, brass is the ideal material to use.
Copper-Tin Alloy (Bronze)
Bronze is unquestionably the most adaptable bearing material, delivering a wide range of properties from a diverse range of alloys and compositions.
It is commonly useful for statues, medals, bells, coins, gears, bearings, bushings, etc.
You can make a bronze alloy casting by adding appropriate proportions of tin and copper during the melting process.
However, it must be ensured that you melt tin first, followed by copper, to avoid flash.
Aluminum casting is the most commonly performed casting, due to its low melting point and good mechanical properties.
Adding alloying elements further enhances its properties, making it suitable for a variety of applications.
Aluminum alloy castings provide high strength, fluidity, excellent machining, low cost, and flexibility to cast using any metal casting method.
It is used for manufacturing structural frames, automobile parts, food trays, cans, and foils, as well as various tools, utensils, and appliances.
Alloying copper with around 1% chromium enhances electrical conductivity, doubles its strength, and improves corrosion and wear resistance.
This makes chromium-copper alloy casting suitable for producing electrical components, resistance welding electrodes, and metal handling equipment.
Zinc alloys outperform aluminum, bronze, magnesium, and cast irons in terms of strength, stiffness, toughness, bearing, machining, performance, and cost of casting.
This makes them suitable for household appliances, mechanical and automotive parts, and musical instruments.
Apart from that, zinc enhances the fluidity of the molten metal, facilitating the proper flow of liquid metal into the mold cavity, thereby enhancing the casting quality.
Different types of nickel alloys can be formed by adding different metals such as copper, chromium, iron, and molybdenum to achieve good strength.
Inconel is a nickel alloy consisting of 14% chromium, and 6% iron. It is useful for applications where high strength and oxidation resistance are needed.
Nickel-based white bronze containing 20% zinc, 20% manganese, and 1% aluminum provides high strength, ductility, and excellent corrosion resistance.
It is useful for plumbing fixtures, hospital equipment, and architectural and marine hardware.
Alloys Casting can produce a unique set of physical and mechanical properties such as strength, machinability, weldability, and corrosion resistance.
The large variety of casting alloys makes it easier to choose the best material for a given application.
If your DIY project demands high corrosion resistance with good ductility, it is recommended to use a copper or aluminum-based alloy casting.
Frequently Asked Questions (FAQ)
Which casting process is most suitable for casting ferrous and nonferrous alloy casting?
Casting processes, such as sand casting, investment casting, or shell casting are best suited for ferrous alloys, whereas die-casting, centrifugal casting, high-pressure casting, investment casting, and vacuum casting are ideal for non-ferrous alloys.
What are the processing steps required before melting non-ferrous metals and alloys?
The processing steps required before melting non-ferrous metals and alloys are - fluxing, metal refining, degassing, deoxidization grain refining, pumping, and filtration.
Can I mix all the metals together?
No, you can not mix all metals together. You may get multiple layers of the metals based on the melting temperature and density of the metal. Furthermore, adding any reactive or toxic material can produce extreme flashes or release toxic gas, further increasing the risk of accidents.
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