M. A. Martínez

Recycling of aluminium alloy and aluminium matrix composite chips by pressing and hot extrusion

Abstract A method for recycling aluminium alloy chips by cold and hot pressing followed by hot extrusion was studied as well as the possibility of using this method to recycle aluminium matrix composite chips. Hot extrusion of cold or hot pressed samples could satisfactorily promote the consolidation of the chips. Hot extrusion of hot pressed samples proved to be the best route, from the point of view of mechanical properties, but, on the other hand, hot extrusion of cold pressed samples route has higher cost profit. Aluminium AA6061 matrix composite reinforced with Al2O3 recycled by cold pressing and hot extrusion was compared with the primary material produced by conventional casting process from which the chips were obtained. Due to the refinement of the microstructure and the dispersion of the aluminium oxide caused by the extrusion process, the ultimate tensile strength (UTS) and the hardness were higher for the recycled material than for the former composite.

Effect of Boron Carbide Filler on the Curing and Mechanical Properties of an Epoxy Resin

The curing process, wear behavior, and mechanical properties of an epoxy adhesive filled with boron carbide (B4C) were studied. Two different particle sizes and amount of reinforcing B4C were tested. One advantage of using B4C is its ability to absorb neutrons, a property of great importance in the nuclear industry. Gel time and degree of curing were measured to evaluate the effect of adding B4C to the epoxy resin. The chemical structure was studied by Fourier Transform Infrared Spectroscopy (FTIR) and the B4C distribution was analyzed by laser confocal microscopy. Dynamic Mechanical Thermal Analysis (DMTA) tests were also carried out to monitor the viscoelastic properties and the glass transition temperature (Tg) of the cured reinforced epoxy. The wear resistance against alumina was measured using a pin-on-disc test, evaluated as mass loss. The wear tracks were studied by Scanning Electron Microscopy (SEM). The bending strength was also studied to assess the degree of interaction between the B4C and the matrix. The results showed that the reinforced epoxy with B4C was very abrasive, wearing the alumina. The reinforced epoxy had excellent mechanical properties that increased with B4C content and with small particles. Moreover, the Tg value decreased slightly upon B4C addition.

Recovered slate waste as raw material for manufacturing sintered structural tiles

Since roofing slate exploitations generate large quantities of slag from the quarry and mud from the cutting tools, special efforts are needed to avoid associated environmental hazards, such as floods and the unsightliness of slag-heaps. Recovering this mud and slag as raw material for manufacturing sintered structural parts could be a response to the demand. This study, which includes a characterisation of the material and an evaluation of the final properties, examines the raw material and its behaviour during compaction to determine whether it is suitable for processing by powder technology. A mineralogical characterisation by chemical analysis and X-ray diffraction, together with a thermal analysis, provided the data of the sintering process. The properties of the sintered samples were checked by: density, dimensional change, volume loss, mass decrement, three-point bending strength, water absorption and permeability, and wear behaviour trying to guarantee their behaviour.

TiCN—high speed steel composites: sinterability and properties

Metal matrix composites, based on M3/2 high speed steel and reinforced with two different percentages of TiCN (2.5 and 5 wt%), were manufactured following a conventional powder metallurgy route: mixing, compacting and sintering. The carbide and base material powders were dry mixed and uniaxially compacted at 700 MPa. After this, vacuum sintering was carried out at different temperatures to study the sinterability of manufactured composites. Effects of sintering temperature on sintering density, dimensional change and hardness with temperature were measured, and this study was completed with a dilatometric analysis. Materials were sintered at optimum sintering temperature (1275 °C), and transverse rupture strength and wear behaviour of sintered materials was examined.

Influence of carbon and aluminium additions on the Fe–10% B (wt.) system

Abstract This work studies the influence of sintering temperature on microstructure and X-ray diffraction patterns of Fe–10% B (wt.) system. The way to obtain these materials is powder metallurgy (P/M) (mixing elemental powders, uniaxial compacting and sintering). Thermal analysis was carried out through dilatometry and differential thermal analysis (DTA). All heat treatments were carried out in argon to avoid steel deborizing. Studied temperatures vary from 1120 to 1400xa0°C. The influence of carbon (between 0.3 and 0.6xa0wt.%) and aluminium (4xa0wt.%) additions were also studied. Microstructural evaluation (optical microscopy and scanning electron microscopy) was done, studying reactions between boron and iron.

Aging by moisture and/or temperature of epoxy/SiC composites: Thermal and mechanical properties

The present work focuses on investigating the effects of moisture absorption on the mechanical and thermal properties of epoxy reinforced with percentage (by wt.) silicon carbide (nano and micro-metric) composites. In order to quantify the effect of moisture and temperature on aging, the specimens were exposed to three aging conditions for 30 days. Variations of Tg (glass transition temperature), water absorption, and mechanical properties were determined as a function of exposure time. In composite materials, aging depends on the exposure conditions, such as amount of absorbed water, temperature, and oxygen concentration. All these factors affect the thermal and mechanical properties. At room temperature and 95% relative humidity, plasticizing and swelling occur, with mechanical properties loss. At 60℃ and 5% relative humidity, polymeric chains crosslink resulting in mechanical properties improvement; Tg and thermal conductivity increase. At 60℃ and 95% relative humidity, the time required to reach saturation decreases when compared to room temperature evaluated condition, as the exposure temperature increases.

Structural and Mechanical Characterization of γ-Methacryloxypropyltrimethoxysilane (MPS) on Zn-Electrocoated Steel

Anaerobic adhesives have found an extensive use in many applications in mechanical engineering as sealers, threadlockers and retainers on metal surfaces. These adhesives have shown a good performance with threaded components with Cr[VI] coatings. Hexavalent chromium is a carcinogenic material so its use is limited or prohibited by environmental regulations in several countries, such as the United States and the European Union. In order to avoid this problem, non-chromated zinc coatings are used. However, anaerobic adhesives are not very effective with these types of coatings. Silane coupling agents could be an alternative to improve the performance of these coatings with anaerobic adhesives. The aim of this work was to investigate the effect of a silane treatment on Zn-electrocoated steel. H1-NMR (proton nuclear magnetic resonance) studies of γ-methacryloxypropyltrimethoxysilane (MPS) hydrolysis provide the optimal conditions for silane application onto substrates. Analysis of silane layers over zinc coatings was performed by means of Fourier Transform Infrared (FT-IR) spectroscopy. In addition, single lap shear tests were used to compare the strength of anaerobic adhesive joints on Zn-coated specimens with different surface treatments. NMR shows that maximum hydrolysis of MPS takes place at 150 min. Adhesive joints prepared using MPS coatings after this hydrolysis time give maximum shear strength.

Preparation of aluminium boride by powder technology

The problem with using boron in a sintering process is the formation of a surface layer of oxide [Combust., Explosion Shockwaves 10 (1974) 539] which hampers the process. The incorporation of reducing elements into the amorphous boron is done by powder technology. Suitable working conditions were designed to provide sintered boride free of oxide. The reducing elements served the double purpose of forming borides and of avoiding the formation of boric oxide in the first stage of sintering. Hermetically sealed crucibles were designed for the sintering by thermal shock. The source materials were amorphous boron and atomized aluminium.

Sintering stainless steels with boron addition in nitrogen base atmosphere

Stainless steel has become increasingly used in the nuclear industry recently. Thus, this study is aimed at investigating stainless steel 316L with boron addition and the possibility of sinter these materials in nitrogen rich atmospheres. By analyzing the final product, the properties of the stainless steel 316L (good mechanical properties and high corrosion resistance) with the boron neutron absorption properties were found to unify. The P/M technologies enable higher boron quantities to be added to the steel. This was not possible with the solidification conventional technologies, as segregation is produced in the latter. Mixtures with 0.75 and 1.5% boron were prepared. Uniaxial compaction (at 700 MPa) was carried out to study the green density of compacted materials. The sintering atmosphere used was N2-10%H2-0.1%CH4, and was used to form boron nitrides instead of chromium nitrides. Although some boron nitride was formed, not all chromium nitride formation was avoided. The sintered samples were characterized through their physical properties (density and dimensional change), chemical analysis (carbon and nitrogen contents), mechanical behavior (bending strength and hardness) and wear behavior. To finish the materials characterization, a microstructural study is proposed. Lastly, the wear tracks were observed by SEM. Boron nitride has precipitated in grain boundaries, making more difficult the sintering of the material and reducing the properties of the stainless steel.

Analysis of shear strength of cylindrical assemblies with anaerobic adhesives using Weibull statistics

A statistical method to study the reliability of cylindrical anaerobic adhesively-bonded assemblies is presented in this work. An anaerobic adhesive was used to manufacture four groups of bonds with different gaps, but with the same surface pre-treatment and curing position. Shear strength values were obtained and used to determine reliability of all adhesive bonds using the Weibull statistical distribution. Although the Weibull analysis has been widely used in the study of composite materials, its application in adhesive bonds is being explored now. A two-parameter Weibull distribution was employed to execute the Weibull analysis, using an estimator that renders a more realistic Weibull modulus value, as other estimators were found to subestimate or overestimate this value. Weibull modulus values were obtained for adhesive bonds with different gaps to study their reliability, and these results have been compared with the shear strength results.