There are differences between forged vs cast material. The basic difference between forging and casting is that the forging process does not melt the work piece material to create a new shape. In casting, metal is melted and poured or forced into a mold made in the shape of the desired item. In forging, deformation of the material in solid form, often by hammering or pressing the material, creates the desired shape. Both processes have certain advantages that may lead to one or the other being used to create a component depending upon cost and service use requirements. Aluminum and aluminum alloys are subject to the same metallurgical principles as other metals which will determine which process provides the advantage for a given end-use item.
When metal is melted and casting is produced, a product of complex shape can result, only limited by the mold making and the flow and solidification dynamics of the metal. This allows casting to economically produce components with internal chambers and external features that reduce the number of subsequent metal removal operations performed to complete a finished part. The disadvantage is the potential for contamination while metal is in a liquid state from impurities entering into the liquid. Formed while ingots and additives are being melted, impurities may not be sufficiently filtered from the liquid metal as it flows into the mold. Small pieces of the conduits leading to the mold or the mold itself can also flake or break, entering the liquid. Turbulence as liquid metal flows through complex chambers may result in voids and internal, hidden, areas of non-fill. Alloy segregation while the metal is in liquid form can result in inconsistent material properties from one area of the casting to another. Defects such as tears or cracks can form when different sections mass cools at different rates as the metal solidifies.
Forging has the advantage of the addition of deformation energy to further refine and improve the metallurgy of the shape being created. Through mechanical and thermomechanical deformation energy applied, originally cast ingots of aluminum are shaped and reshaped, changing the internal microstructure. Any inclusions or alloy concentrations are dispersed, and any voids are crushed and eliminated. Forging energy drives the recrystallization of the microstructure, creating enhanced durability and toughness. Forgings are not usually able to produce shapes as complex as castings. This often requires additional finishing operations which adds to the cost of using forgings, compared to castings. The improved properties of forged product outweigh cost issues, however, when safety, reliability and the cost of component failure are the greatest challenges.
Forging Aluminum into Alloys
An additional advantage of forging is the ability to form and shape alloys consolidated from metal and other additive powders. Alloys and matrix materials of this type are produced and consolidated as powders as the constituent elements cannot be successfully melted and cast. Thermomechanical energy is often the most practical means to consolidate powders into solid form. Deformation processes such as forging are then used to further shape these materials, in a solid state, to more useful, near net forms, providing improved economy for use of these more expensive materials. In this way, forging is ensuring the capability and usability of materials that provide properties that will meet future design challenges.
Forged products will be the choice when components must exhibit maximum properties and durability in service, where weight and mass must be minimized and failure would be costly or catastrophic. Other processes seek to claim “wrought properties” but only the forging process can consistently and reliably supply it.