Abstract:
Minor variations in alloy composition are the primary
causes of casting rejects and occur even when the normal process conditions
prevail. These variations impact significantly in microstructure
and mechanical properties of aluminium alloy castings. Therefore, it
is necessary to closely control the alloy composition and molten metal
quality.
Al-Si alloys are light-weight structural materials which play an important
role in vehicle weight reduction and improving fuel economy
in automobile industry. Currently, 85 percent of aluminium castings
are used in the automobile and aerospace industry due to the unique
casting properties and mechanical strength.
Unfortunately however, Al-Si alloy castings are known to suffer from
presence of iron that greatly undermine their mechanical properties
such as impact energy and fatigue strength. Finding an innovative
solution that reduces the effects of the presence of iron is an area of
increased research interest.
In this paper, the effects of additive elements on the impact and
fatigue strength of the aluminium alloy castings from wheels were
investigated. The aluminium wheels were melted in an oil fired
furnace and the metal poured into 4 kg ingots. A sample was collected
in a carbide crucible, quenched and used to obtain the alloy chemistry.
The ingots were re-melted at 7500C and poured into a sand mold.
This procedure was repeated with variations of strontium, iron and
manganese elements. The castings were then machined according to
ASTM-E8 standards for the impact specimen and ASTM-E466-82
for the fatigue specimens.
The results depicted that Strontium addition increased both the fatigue
life and impact strength of the alloy, while iron addition reduces.
However, addition of manganese neutralized the detrimental effects
of the iron.
