M.I. Barrena

Dissimilar fusion welding of AA7020/MMC reinforced with Al2O3 particles. Microstructure and mechanical properties

Abstract Metal matrix composites reinforced with Al 2 O 3 particles combine the matrix properties with the ceramic properties of the reinforcement. However, its wide application as structural materials need of the proper development of their joining processes. The present work describes the results obtained from microstructural (Optical and scanning electron microscopy and electron probe microanalyser) and mechanical evaluation (hardness and tensile tests) of aluminum matrix composites (AA7005) reinforced with 10% vol. fraction Al 2 O 3 particles (W7A10), welded to the unreinforced alloy AA7020 (Al–Zn–Mg), using metal inert gas welding process using ER4043 (Al–Si) and ER5356 (Al–Mg) as fillers. The thermal effect of welding on different types of joint results in a loss of the mechanical properties in the heat affected zones. These properties could be recovered with post-welding heat treatments.

The influence of Si and Mg rich phases on the mechanical properties of 6061 Al-matrix composites reinforced with Al2O3

Besides altering the kinetics of precipitation, the reinforcements with alumina particles appear to alter the relative proportions of the various phases formed in the matrix alloy during ageing. Alumina also seems to reduce the volume fractions of hardening phase in these materials, especially at higher contents. One reason for this effect could be the dislocation relief of the matrix strain associated with the early precipitates. Additionally, the diffusion of Mg and its subsequent incorporation into the reinforcement at the Al2O3/Al interface could also result in Mg depletion from the matrix, accounting for the reduction of the β (Mg2Si) particle sizes. Magnesium incorporation into interfacial alumina to form MgAl2O4 has been observed in these materials. This paper shows that the nature and morphology of the second phases depend the heat treatment conditions on.

Conductive CNF-doped laminates processing and characterization

In this study, carbon nanofiber (CNF)/glass fiber/polyester resin laminated composites were prepared using two different manufacturing methods: Hand lay-up method and vacuum bagging. These techniques were used in order to compare their influence in the final properties of the composite. Every kind of laminate was loaded with CNF between 0 and 2 wt% with respect to the resin weight. It was found that the presence of CNF produced a reinforcement of the composites in both flexural and tensile strengths regardless of the manufacturing method. On the other hand, composites prepared by the vacuum bag technique showed an important increase in their mechanical properties due to the preparation method. Finally, the CNF-loaded laminates were found to be conductive with only 0.5 wt% CNF loading.

Protection behaviour of surface films formed on AZ91D magnesium alloy in nitrogen/1,1,1,2-tetrafluoroethane atmospheres

Protective surface coatings on an AZ91D magnesium alloy were formed in an atmosphere mixture of nitrogen and 1,1,1,2-tetrafluoroethane (HFC-134a). The surface composition and microstructure were characterized using X-ray diffraction analysis and scanning electron microscopy, respectively. The cross-section morphologies of the coatings show that an increase in conversion time results in an increase in the continuity and compactness of the coating generated on the surface of the AZ91D alloy. The corrosion resistance tests performed by immersion into 3.5% NaCl solutions were investigated by electrochemical measurements. The results showed that the coated samples had higher corrosion resistance than the uncoated alloy. On the other hand, the corrosion density of the coated samples decreased by increasing the conversion time by about two orders of magnitude, compared with the un-coated samples. This behaviour is attributed to the formation of a protective surface film constituted mainly for MgF2, together with other phases. The nature of these phases depends on the process conditions.

Welding of AA6061-(Al2O3 )p composite: effect of weld process variables and post-welding heat treatment on microstructure and mechanical properties

Abstract Metal–matrix composites reinforced with Al2O3 particles combine the properties of the matrix (ductility and toughness) with the ceramic properties of the reinforcements (high strength). However, their wide application as structural materials requires a proper development of their joint process. The present work describes the results obtained from microstructural (optical and scanning electron microscopy) and mechanical evaluation (hardness and tensile tests) of the welded aluminium–matrix composite (AA6061) reinforced with 10% and 20% volume fraction Al2O3 particles (W6A10 and W6A20, respectively) using the MIG (metal inert gas) welding process and ER5356 (AlMg5) as filler material. A characteristic of the welds carried out in composites is that the size of the melt pool is wider than in the unreinforced materials, for the same welding conditions. This is caused by the lower thermal conductivity of the composites. Furthermore, composites act as an insulator reducing the cooling rate of the bath. The thermal effect of welding on different types of joints results in a loss of the mechanical properties in the heat affected zones (HAZ). These properties can be recovered with post-welding heat treatment.