Joining of carbon fibre reinforced polymer (CFRP) composites and aluminium alloys – A review Part A Applied science and manufacturing

Enhancing the solid-state joinability of A5052 and CFRTP via an additively manufactured micro-structure

Pinless friction spot joining (FSpJ) has proven to be a competitive friction-based joining technique for fabricating metal/carbon fiber-reinforced thermoplastics hybrid joints. The present study investigated the feasibility of tool modification to improve the property of the silane-coated 6061-T6 Al alloy and carbon fiber-reinforced polyamide-6 (CF/PA6) FSpJ joint. The interfacial structure, bonding strength and fracture surface of the joints obtained by four tools, viz, old flat (OT), new flat (NT), concave-shaped (CT) and ring-shaped tools (RT) with different rotation speeds, were analyzed and compared. An experimentally validated three-dimensional finite element model was also built to help understand FSpJ process. Despite modifying the tool shape, covalent bonding predominated the interfacial bonding force where the formation of nanoscale diffusion layers was witnessed with no new type of covalent bonds generated. The resultant fracture surface was dominated by the cohesive failure mode, suggesting strong chemical bonding between the re-solidified resin and silanized Al surface. The decrease in tensile shear force in the case of NT was due to the extensive formation and coalescence of microscale voids and porosities. This was mitigated by using CT and RT tools, from which the heat input was controlled leading to a more homogenized heat field. From the combined evaluation of thermal process and mechanical characteristics, CT tool was recommended for the FSpJ of Al and CF/PA6 because it offered a more uniform temperature distribution and improved macro-mechanical interlocking at the interface with good wetting conditions, sufficient chemical reaction and effective joining area, and lower tensile residual stresses, in comparison with other tools, and hence showed the highest shear force. 

Improving bonding strength of Al/CFRTP hybrid joint through modifying friction spot joining tools

Fabrication of micron-sized protrusions on metal surface for metal/polymer easy-disassembly joining by selective laser melting technology

Surface pre-oxidation for enhancing laser assisted joining between carbon fiber reinforced thermoplastic composites and AZ31B Mg alloy

Surface micro−structure for joining with thermoplastic parts was additively manufactured on an aluminum alloy (A5052) substrate by laser scanning on Al−Ti−C powder mixtures. The micro−structure consisted of particle−shaped protrusions with a few hundred micrometers. The effect of C content in Al−Ti−C powder mixtures on the micro−structure and constituent phases was investigated. The fraction of particle−shaped protrusion reached maximum when the C/Ti molar ratio was 0.8. Adhesiveness between the particle−shaped protrusions and A5052 substrate decreased drastically when the C/Ti molar ratio increased from 0.6 to 0.8. Changes in these structural factors were related to the formation of TiC and Al3Ti phases after the laser−irradiations. The A5052 substrate was joined with Polyamide−6 sheets via the micro−structure by hot−pressing. When the C/Ti molar ratio was 0.6, the joint strength reached maximum since both the fraction of particle−shaped protrusions and adhesiveness between particle−shaped protrusions and A5052 substrate were high. The constitute phases (TiC and Al3Ti phases) in the micro−structures were assessed by Scheil simulation for Al−Ti−C system to calculate the component partitioning and solidification path during solidification. These results were used to discuss the relation between the surface micro−structure and powder compositions.

Control of surface micro−structure for Al alloy/polymer joining fabricated by laser process using Al−Ti−C powders: Effect of powder composition.

The effect of stress on irradiation responses of highly oriented pyrolytic graphite (HOPG) was studied by combing molecular dynamics (MD) simulation, proton irradiation, and Raman characterization. MD simulations of carbon knock-on at energies < 60 eV were used to obtain average threshold displacement energies (E¯d) as a function of strain ranging from 0 to 10%. Simulations at a higher irradiation energy of 2–5 keV were used to study the effect of strain on damage cascade evolution. With increasing tensile strain, E¯d was reduced from 35 eV at 0% strain to 31 eV at 10% strain. The strain-reduced E¯d led to a higher damage peak and more surviving defects (up to 1 ps). Furthermore, high strains induced local cleavage around the cavities, as one additional mechanism of damage enhancement. Experimentally, HOPG film was folded, and the folded region with the maximum tensile stress was irradiated by a 2 MeV proton beam. Raman characterization showed significantly enhanced D to G modes in comparison to the stress-free irradiation. Based on the strain dependence of E¯d and the Kinchin–Pease model, a formula for displacement estimation under different tensile strains is proposed. The stress effects need to be considered in graphite applications in a reactor’s harsh environment where both neutron damage and stress are present.

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Seung−Gwang Kim

Papers

Enhancing the solid-state joinability of A5052 and CFRTP via an additively manufactured micro-structure

Control of surface micro−structure for Al alloy/polymer joining fabricated by laser process using Al−Ti−C powders: Effect of powder composition.

Effect of Stress on Irradiation Responses of Highly Oriented Pyrolytic Graphite