J. Rams

Role of Laser Cladding Parameters in Composite Coating (Al-SiC) on Aluminum Alloy

The effect of the different control parameters on the laser cladding fabrication of Al/SiCp composite coatings on AA6082 aluminum alloy was analyzed. A high-power diode laser was used, and the laser control parameters were optimized to maximize the size (height and width) of the coating and the substrate-coating interface quality, as well as to minimize the melted zone depth. The Taguchi DOE method was applied using a L18 to reduce the number of experiments from 81 to only 18 experiments. Main effects, signal-noise ratio and analysis of variance were used to evaluate the effect of these parameters in the characteristics of the coating and to determine their optimum values. The influence of four control parameters was evaluated: (1) laser power, (2) scanning speed, (3) focal condition, and (4) powder feed ratio. Confirmation test with the optimal control parameters was carried out to evaluate the Taguchi method’s effectivity.

Laser Cladding of In Situ Al-AlN Composite on Light Alloys Substrate

In situ metal matrix composites are novel composites in which the reinforcement is formed within the parent alloy by controlling chemical reactions during the composite fabrication. In recent years, there have been attempts to produce AlN composites utilizing the reactions between molten Al and a reactive gas. However, the conventional processing methods are sub-optimal and result in porosity, interface matrix-reinforcement deterioration, and high processing costs. The aim of this research is to develop a methodology to manufacture good-quality in situ Al-AlN composites in a cost effective way. In situ Al-AlN composite was synthesized with a laser cladding equipment. This composite powder can be directly deposited as coating on aluminum alloys conventionally used in the transport sector. The increase in the coatings tribological properties was demonstrated.

Carbon Nanotubes for Assessing the Structural Integrity of Composite Bonded Joints with Film Adhesives

This work analyses the capability of the application of self-sensing film adhesives for assessing the structural integrity of typical aeronautical bonded joints without altering its mechanical behavior. Tests have been carried out on carbon fiber reinforced polymer composites (CFRP) although the method has been also validated on aluminum substrates, showing that different types of strain and damage are detected depending on the characteristics of the joined materials. In both cases, the structural health monitoring of the bonded joints has been achieved. The developed technologies are based on the addition of carbon nanotubes (CNT) to the film adhesives in order to provide electrical conductivity to the different interfaces. The high conductivity and relative large aspect ratio of CNT result in percolation thresholds around 0.1% weight of carbon nanotubes in the adhesive. The CNT network formed in the adhesive offers significant potential to develop sensing for damage detection and health monitoring using direct-current measurements. Loads applied over the nanodoped adhesives produce damage (i.e. cracks, delaminations,…) appearance and/or damage progression in the material, that modifies the integrity of carbon networks and increases the electrical resistivity of the adhesive. Two different methods have been developed to deposit CNTs on film adhesives: innovative inkjet printing methods and mask methods. In both cases the CNTs used were stabilized in water solution to use a solvent that did not damage the behavior of the adhesive. Then, the CNT solution was incorporated in the nanoreinforcement with controlled geometries over the films, providing local and controlled sensitivity to the bonded joints and giving information of the location of the damages, their characteristics and their propagations in an accurate way. doi: 10.12783/SHM2015/270

Relationship between Laser Parameters - Microstructural Modification - Mechanical Properties of Laser Surface Melted Magnesium Alloy AZ91D

Laser surface melting is a high-energy surface treatment that allows modification of the microstructure and surface properties of Mg alloys. In the present work, a high-power diode laser has been used to study the microstructural and mechanical modifications that occur when laser surface treatments are applied to the surface of the AZ91D Mg alloy. Laser-beam power in a range of 375-600 W and laser scanning speeds of 45-60-90 mms-1 has been used to develop a range of laser surface melting treatments. By controlling the laser parameters, two types of surface modifications can be obtained. Complete laser surface melting takes place at high laser input energies whilst at low laser input energies, selective laser surface melting occurs with modification of only one phase in the microstructure of the alloy; the other phase remained unaffected. In terms of mechanical properties, the microstructural modifications introduced by the laser surface treatment implied a hardness homogenization along the melted region.