|
Particle Hardening of Aluminum
Aluminum is now a material of choice for some diesel engines, primarily because revised hardening techniques make it very durable and heat resistant Figure 6. A hardening process performed shortly after the head is cast, called T6 treatment , relieves casting stresses and creates a more uniform metallurgical structure. T6 treatment involves heating the casting to 1000° F (538° C) for about 6 hours and then quenching the casting in water for a few seconds. The cooled casting is then seasoned in a 320° F (160° C) oven for approximately 5 hours and then allowed to cool to ambient temperature. The result is a casting with Rockwell hardness (HRC) on the B scale of approximately 84–88. Another name for this aluminum hardening process is precipitation , or particle hardening . Particles of specialized alloys, such as copper, are mixed into the molten aluminum during the casting process. The rapid quenching in water enables the copper particles to interfere with the arrangement of aluminum atoms in a crystalline lattice, which in turn makes aluminum less brittle but harder at the same time.
|
|
FIGURE 09-6: The popular Duramax diesel uses aluminum cylinder heads.
|
