Given two equal masses of aluminum and cast iron; aluminum is able to absorb twice as much heat energy as cast iron for an equal rise in temperature. This allows an aluminum brake disc to be half the weight of the cast iron disc and still have the same thermal storage capacity.
Aluminum has a thermal conductivity that is up to 4 times greater than cast iron. This has multiple benefits in braking.
Brake Dynamometer Testing
Metal Matrix has conducted and continues to conduct significant on-vehicle and dynamometer testing to ensure the performance, durability and longevity of the Alumatrix brake disc. Testing has been conducted in-house and also at third party testing facilities. The Alumatrix brake disc has been extensively tested on a modified AK Master friction test, as well as the SAE J2928 Thermal Cracking test. Through these tests, we have been able to verify that our brake discs are durable and provide reliable friction. If you are interested in the performance details, you can download test reports below.
Prototype Disc and Pads
A prototype brake disc has been developed based on the geometry of the rear disc found on the 2013-present Ford Fusion. This solid cast iron disc was used as the bench mark for testing. The MMC prototype was manufactured to the identical dimensions of the cast iron brake disc.
With the geometry of the cast iron and Alumatrix disc being identical, the volumes are also identical. Aluminum has a density 1/3 of cast iron, so with equal volumes, a weight savings of greater than 50% is achieved. This therefore reduces the heat capacity ratio, giving the Alumatrix Brake a heat capacity ratio of less than one. In order the match the heat capacity ratio’s the geometry of the Alumatrix rotor would have to change to increase the volume and weight. An equal heat capacity ratio would provide a weight savings of about 50% on a rear disc.
Protype Disc Dimensions
(revolved section view)
Standard off the shelf NAO pads were used against the cast iron disc while an organic pad, developed by a collaborating partner was used against the Alumatrix disc.
Rotors were tested with a dyno inertia of 40 kg∙m2
Thermal Cracking Test
The SAE J2928 Thermal Cracking test is a very intense braking test designed to test the disc’s ability to handle thermal stresses during high power braking events. This test runs 150 cycles (300 stops) from 160 kph (100 mph) down to 0.5 kph (0.3 mph) at a constant deceleration rate of 5.0 m/s2. The first stop is initiated when the brake disc reaches 100°C (212°F). At the completion of the first stop, the disc then cools for 70 seconds while it spins back up to 160 kph (100 mph). After 70 seconds, the second stop is initiated. The disc then cools down to 100°C (212°F) and the cycle is repeated.
Multiple Alumatrix brake discs have run through 300 or more of these high power stops with 40 kg∙m2 of inertia and show no signs of cracking. Maximum operating temperatures reached near 400°C (752°F), which will be considered the maximum temperature threshold. The figure to the right shows an Alumatrix Brake that has done over 1000 stops.
Cast iron discs crack due to their inability to conduct heat away, but with aluminum, the difficulty becomes going over 400°C (752°F). At this point, the aluminum will soften at the disc/pad interface causing smearing and destruction of the transfer layer.