Aluminum Alloys for Automotive Knuckle Castings

Knuckle castings for the automotive industry have traditionally been made from ductile iron, but engineers are now looking to aluminum castings as a lightweight alternative. Amcast Automotive has been involved in the development and manufacture of A206 aluminum knuckle castings since 1989 when it first supplied Aluminum castings for Ford Motor Co. (MN-12 platform). Recently, several new high volume automotive knuckle castings have been introduced using A356 aluminum alloy with T-6 temper.

This paper presents mechanical property information on both A206 and A356 aluminum alloys to assist engineers in the design of knuckle castings in aluminum. In addition to microstructural evaluation, mechanical properties will be obtained from test bars cut from actual heat-treated knuckle castings. Mechanical property information will include:

• Room temperature tensile, yield, and elongation values from mini-test bars (from knuckle castings)
• Elevated temperature tensile, yield, and elongation values from mini-test bars
• High frequency axial fatigue test data.
• Hardness

The A206 aluminum alloy is expected to exhibit superior mechanical properties compared to the A356 aluminum alloy. In A206 aluminum alloy higher strength is achieved both at room temperature and at elevated temperatures because of higher copper and lower silicon contents. Similarly, A206 alloy may show a fatigue advantage for the same reason. Regardless of the property values, both these aluminum alloys are suitable for automotive casting production usage and this this information is intended to assist suspension a knuckle designer in switching from iron to aluminum.