抄録
Hybrid Fiber-Reinforced-Metals (FRMs), in which particulates and whiskers were distributed among the continuous fibers, were prepared by squeeze casting process.
Pure aluminum and Al-5%Mg alloy were used as the matrix metal. The residual expansions were measured and the transverse strength after thermal cyclings between room temperature and 573 K were evaluated. The effects of hybrid technique and alloying element Mg on the thermal fatigue behavior of FRMs were investigated.
The results are as follows:
(1) Approximately 1% of strain of transverse residual expansion was observed after thermal cycling of 1000 times. Aluminum-magnesium matrix composites expanded linearly, while pure aluminum matrix ones expanded nonlinearly.
(2) A lot of cracks between fiber and matrix were observed after thermal cycling. In the case of the non-hybrid composites, many fiber-to-fiber contacts were observed because the fibers were closely packed by the pressure of the molten metal. On the other hand, in the case of the hybrid composites, few fiber-to-fiber contacts were observed because particulates or whiskers existed around the fibers. So, some cracks were connected through fiber-to-fiber contact points for the non-hybrid composites in contrast with cracks separated around each of fibers for the hybrid ones.
(3) During thermal cycling of aluminum-magnesium matrix composites, the transverse strength of the composites was promptly degraded from 100 to 80 MPa for the hybrid composites and it gradually fell down from 45 to 30 MPa for the non-hybrid ones.
(4) Few fibers debonded from matrix of hybrid composites on transverse fracture surfaces in contrast with the non-hybrid composites which indicated a lot of debonded fibers.
