Zinc alloys are preferentially cast by

Explanation:

Zinc Alloys are preferably cast by Die Casting.

Casting: It is a manufacturing process in which liquid material is filled into the mold, which contains a hollow cavity of the desired shape and then allowed to solidify. The solidified part is known as a casting, which injected or broken out of the mold to complete the process.

Die Casting:  Die casting is a manufacturing process for producing accurately dimensioned, sharply defined, smooth, or textured surface metal parts. It is accomplished by forcing molten metal under high pressure into reusable metal dies

• Die casting produces parts that are durable and dimensionally stable while maintaining close tolerances. They are also heat resistant
• Die-cast parts are stronger than plastic injection moldings having the same dimensions.
• In Die Casting major form of Alloy used is Zinc Alloy.

Additional Information

Investment Casting: 

• It is a wax or suitable polymer pattern is coated by dipping into the refractory material slurry.  
• Once the refractory material coating is hardened then this dipping process is repeated several times to increase the coating thickness and its strength.
• Once the final coating is hardened the wax is melted out and molten metal is poured into the cavity created by the wax pattern.
• Once the metal solidifies within the mould, metal casting is removed by breaking the refractory mould.

Centrifugal Casting: This is a process where the mold is rotated rapidly about its central axis as the metal is poured into it. Because of the centrifugal force, continuous pressure will be acting on the metal as it solidifies.

• The slag, oxides, and other inclusions being lighter gets separated from the metal and segregates toward the center.
• There are three main types of centrifugal casting processes. They are,

1. True centrifugal casting,
2. Semi-centrifugal casting, and  
3. Centrifuging. 

Shell-mould Casting: It is a process in which the sand mixed with a thermosetting resin is allowed to come into contact with a heated metallic pattern plate so that a thin and strong shell of mould is formed around the pattern.

• Then the shell is removed from the pattern and the cope and drag are removed together and kept in a flask with the necessary back-up material and the molten metal is poured into the mould.
• Generally, dry and fine sand that is completely free of the clay is used for preparing the shell moulding sand.
• The grain size to be chosen depends on the surface finish desired on the casting.
• Too fine a grain size requires a large amount of resin which makes the mould expensive.