Casting Defects of Metal Materials, part 4

The main defects of casting products are segregation, pores, shrinkage and shrinkage, inclusions, cracks, cold shut and other defects.

Inclusions

Metals or non-metallic materials with obvious interfaces and greatly different properties from the matrix are called inclusions.

According to the nature of the inclusions, they can be divided into two categories: metal inclusions and non-metallic inclusions. Metal inclusions refer to various metal compound primary crystals that are insoluble in the matrix metal, unmelted high-melting point pure metal particles, and foreign foreign metals; non-metallic inclusions include oxides, sulfides, carbides, fluxes, slags, coatings, furnace lining debris, and silicates.

According to the different sources of inclusions, they can be divided into endogenous inclusions and exogenous inclusions.

Endogenous inclusions may exist in a free state or in a state of combining with the matrix metal to form a compound, or they may be a combination of multiple impurities.

The high-melting point metal compound primary crystals or pure metals that precipitate first in the endogenous inclusions are mostly regular granular, blocky, flake or needle-shaped, and the distribution is extremely uneven.

Low-melting point metal compounds often precipitate along the grain boundaries or dendrite axes in the form of liquid droplets, spheres, networks or films. During pressure processing, inclusions with good plasticity can be stretched and deformed along the processing direction, while inclusions with poor plasticity still maintain the shape during casting or break into smaller particles, distributed in the form of discontinuous chains along the processing direction.

Foreign inclusions are flakes from the furnace lining and tools during the production process, usually coarse and irregular in shape. Because they have completely different chemical compositions and structures from the matrix, they can be found at the fracture or during cutting according to different colors and corrosion conditions.