PURPOSE: To relieve the stress caused at the boundary between an arbor and base metal at the time of casting-in or the heat treatment thereafter and to prevent the occurrence of peeling and cracking by forming the aluminum alloy arbor formed by reinforcing a cast-in arbor with NiTi shape memory alloy fibers having the coefft. of thermal expansion approximate to the coefft. of thermal expansion of the base metal.

CONSTITUTION: The NiTi shape memory alloy fiber reinforced aluminum alloy core is formed in place of the Si whisker reinforced aluminum alloy arbor used from heretofore. The arbor is arranged in at least the stress concentrating part of the casting and is cast-in with the aluminum or 6061 aluminum alloy. As a result, the stress does not remain between the arbor and the base metal and in addition, the rupture strength and fatigue strength of the aluminum casting are improved by the plasticity of the NiTi alloy. The arbor is preferably formed by uniaxially orienting the NiTi shape memory alloy fibers in a range of 5 to 70vol.%, more preferably 25 to 70vol.% in the aluminum alloy.