Aluminum Alloys for Automotive Disc Brake Calipers

Disc brake calipers for the automotive industry have traditionally been made from ductile iron, but more of the calipers are currently being converted to aluminum, with weight savings of nearly 40 percent. Amcast Automotive has been involved in the development and manufacture of aluminum caliper castings since 1984 when it first supplied service production aluminum caliper castings for the four-wheel disc brake Pontiac Fiero. Presently, Amcast is introducing several new high volume automotive calipers using heat-treated aluminum 354 and 357 alloys.

The paper presents alloy optimization and mechanical property information of aluminum 354 and 357 alloys to aid brake engineers in the design of calipers. In addition to microstructure evaluation, mechanical properties obtained from test bars cut from actual heat-treated caliper castings are presented. The mechanical property include:

• Room temperature tensile, yield, and elongation values
• Elevated temperature tensile, yield, and elongation values
• Axial fatigue strength values
• Hardness

The two alloys exhibit similar room temperature properties with 354 showing marginally higher values. The elevated temperature tensile values of 354 alloy is slightly higher because of its higher copper content. Similarly, 354 fatigue data shows slightly higher values. The 354 alloy has 1% higher density than 357 alloy. However, both of these alloys are suitable for the caliper application. This paper attempts to assist the brake caliper designer in the conversion from iron caliper to aluminum caliper.