Three kinds of material, Al single crystals (Al SX) and a non-directionally or directionally solidified Al-6 mass%Ni eutectic alloy containing Al
3Ni particles or fibres in the Al matrix (Al
3Ni particle/Al or Al
3Ni fibre/Al, respectively), were deformed at room temperature in tension-compression tests, in order to make clear how and why the Bauschinger effect (B.E.) is influenced by the state of dispersion of hard Al
3Ni second-phase.
The degree of B.E. at a given prestrain ε
p was found to be larger in the order of Al SX, Al
3Ni particle/Al and Al
3Ni fiber/Al. TEM observation showed that the tendency of tangled cell-wall formation in the Al matrix decreased (and as a result the density of isolated dislocations increased) in the same order, presumably due to an increasing difficulty of dynamic recovery during straining. On the assumption that the reverse strain after stress reversal is mainly caused by plastic deformation of the Al matrix, the higher back stresses (such as pile-up stresses) and the higher density of reversely-mobile dislocations, both of which may be associated with a uniform dislocation arrangement, can explain why the degree of B.E. increased in the observed order. Further, the degree of B.E. in all the materials examined was uniquely related to the so-called mean internal stress in the matrix 〈σ
M〉 only for a small ε
p (up to which the dislocation distribution was rather uniform); for a larger ε
p, the B.E. depended strongly on dislocation structures in the Al matrix even for a given 〈σ
M〉.
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