International Journal of Materials Engineering and Technology
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Abstract: Aluminium cast alloys,
such as AA333 (Al-8Si-2.4Cu), is widely used for automotive. One application is
cylinder head for motorcycles that are produced through low pressure die casting
(LPDC) process. To reduce rejects due to porosity and shrinkage, molten metal
must have appropriate fluidity to fill up cavity of LPDC die. Fluidity of molten
metal may be enhanced through modification of microstructure by adding Sr. In
this work, we study the effects of Sr addition on the level of modification and
properties of AA333 aluminium cast alloys. Injection temperatures are varied to
observe their effects on modification processes. Fluidity of molten metal is
measured by spiral method, and porosity has been observed through vacuum
porosity tests. Tensile and hardness tests are conducted as well as observation
on the microstructure of the materials in as-cast condition by using light
microscopy and
SEM
(scanning electron microscope) equipped with
EDS
(energy dispersive spectroscopy). The higher the Sr addition, the higher the fluidity
of molten AA333 alloys. Modification of microstructure is apparent by addition
of Sr, in which accicular Si eutectic transforms into fine fibrous, a-Al(Fe, Mn)Si ‘chinese
script’ structures alter into acicular, and pocket phase
changes into massive blocks. Injection temperature seems to have little effects
on the modification of microstructure by addition of Sr. However, Sr seems to
increase porosity which reduces the effectiveness of modification.
Keywords and phrases: AA333, Al(Fe, Mn)Si, low pressure die casting, fluidity, modification.
