Abstract
Mechanical, physical and chemical properties of a part depend on the size, morphology and dispersion
of the constituents of the microstructure of the part’s material. Therefore, this chapter discusses the different
processes of altering the microstructure of Al‐Si based alloys to desired functional properties. These processes,
commonly called modification methods, were broadly categorised into three: chemical, thermal and mechanical
methods. Chemical method, which involves the addition of some elements, in trace levels, to alloys to be modified,
is the best modification option. The elements for modifying are called modifiers. The three commonest used
modifiers (sodium, Na, strontium, Sr and antimony, Sb) were discussed. The chapter, however, noted that for
optimal alloy’s mechanical attributes, thermal treatment is usually combined with both chemical and mechanical
modification processes. Thermal involves rapid cooling of alloy for modification, while mechanical method
depends on force to break up large α‐Al dendrites and plate‐like Si phases.