**4. Conclusion**

402 Recent Trends in Processing and Degradation of Aluminium Alloys

WEDM Carbide Turning Diamond Turning

10 10 10 10 10 10 10 10 10 -9 -8 -7 -6 -5 -4 -3 -2 -1 i (Acm ) -2

Fig. 16. Potentiodynamic polarization curves of the composite machined to different

In the eclectically discharged machined specimen, a resolidified layer of aluminium provided a blanketing effect on the substrate. A reasonable range of passivity was produces on the surface. The high resistance was provided by a layer of oxide on the resolidified aluminium layer created by machining. From the above evidence it is to be understood that surface morphology plays an important role at the Al /SiC interface. Scanning micro reference studies has been employed for direct mapping the active centers on surface of electrode with a low dimensional resolution in micrometers. Evidence of micro pitting has been observed at the open-circuit potentials which were more negative than the pitting potential. In their studies, the same conclusion was reached; i. e the SiC/Al interface is the active center for localized corrosion due to the precipitation of intermetallic compounds

The observation that heat treatment increases corrosion resistance is shown by temper T4 of Al6013 /20 SiC (p), it is further supported by studies on temper T6 of Al2009/SiC (w), which showed a higher resistance to pitting compared to as rolled specimens It has been already stated above their heat treatment induces homogenization which causes a reduction in the concentration of intermetallic compounds and hence, reduces localized

From the above discussion it may be concluded that the composites are more sensitive to pitting than their monolithic counterparts unless they are subjected to T4 or T6 heat treatment. These is sufficient evidence to show AL/SiC interface is the main target of localized corrosion due to the presence of intermetallic particulates and inclusion which may form micro-galvanic cells and induce localized corrosion. It is also observed that SiC




E vs. SCE(mV)




conditions (Yue et al., 2002)

(Zaki, 2000).

Corrosion.

particles are not attacked.

Based on the studies conducted in the last they decades, the following are the major conclusion on the mechanical and corrosion behaviour of Al MMCs


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**17** 

*Russia* 

**Interrelation Between Failure and** 

**Pre-Fracture Zone Under Low-Cycle Loading** 

When structures are loaded in catastrophic mode of operation, localization of irreversible strains occurs in regions of stress concentration. This is caused by the geometry of a structure or by the presence of fetaures (dints, holes, cracks, inclusions with mechanical characteristics different from properties of original material). If loading is in progressing, repeated loads cause gradual degradation of the material in regions of the localization of inelastic strain. As a result, this leads to generation and extension of cracks and to loss of a load capacity of the structure. Study of regularities of material degradation in regions of strain localization will permit one to appreciate possible structure resources in a catastrophic situation or consequence of failure, which affects subsequent behaviour of a structure in a

The distinctive features of fracture surface microrelief of metallic components in fatigue are fatigue striations oriented normally to the crack extension direction. It is appropriate to relate formation of fatigue striations to stepwise crack tip advance, and to record residual deflection of a beam under three-point bending when the loading corresponds to the lowcycle fatigue. A current striation may be formed after several loading cycles due to arrest of a fatigue crack after each advance of its tip in the Laird- Smith model (Laird & Smith, 1962), the material being embrittled in a pre-fracture zone at each loading type. Damage accumulation in the pre-fracture zone is associated with accumulation of inelastic strains in

The aim of the present work was to study damage accumulation in the regions of inelastic strains near the notch tip having a finite width. Two cases are considered: i) symmetric three-point bending of a beam (the edge notch is made on the underside of a specimen in the transverse symmetry plane, damage accumulation is estimeted by the increment of a residual deflection); ii) tension of a plain specimen with a narrow edge notch (direct viewing of fatigue crack propogation was performed using digitized microscope with resolution of about 22500 pxel/mm2). Mechanisms of deformation, damage accumulation and failure of

In the first case, the choice of geometry of a specimen and the loading type are governed by

material under fatigue conditions have been proposed.

the following considerations.

**1. Introduction** 

common regime.

this zone.

Vladimir Kornev, Evgeniy Karpov and Alexander Demeshkin

**Damage Accumulation in the** 

*Lavrentyev Institute of Hydrodynamics SB RAS* 

