Sviluppo di microstrutture in campioni di argento sottoposti a deformazione plastica severa

Il lavoro presenta i risultati di indagini svolte su campioni di Ag commercialmente puro sottoposti adeformazione plastica severa mediante tecnica ECAP e attraverso laminazione asimmetrica a freddo. È statastudiata l’evoluzione della microstruttura e delle proprietà meccaniche al variare della deformazione impartita,rispettivamente mediante tecniche SEM / TEM e attraverso misure di durezza e prove di trazione. L’argentoè stato scelto come materiale rappresentativo dei metalli a struttura FCC con bassa energia dei difetti diimpilamento e quindi elevata possibilità di deformazione assistita da geminati. In letteratura esistono limitateinformazioni sull’evoluzione della struttura ultrafine di questi metalli nel regime di deformazione plasticasevera. I dati vengono discussi considerando l’evoluzione della struttura derivante dalle specifiche tecniche dideformazione e le proprietà raggiunte

Aging behaviour and mechanical properties of a solution treated and ECAP processed 6082 alloy

A study was carried out on the aging behaviour of a solution treated 6082 aluminium alloy deformed by equal channel angular pressing up to six passes. Aging of the so obtained ultrafine alloy was studied by DSC and TEM analyses as well as by isothermal treatments at 130, 160 and 180C. The results showed that the formation of metastable beta double prime and beta prime precipitates were markedly anticipated and that the stable phase was partially suppressed in the alloy processed to 4 and 6 passes, presumably due to anticipated precipitation of Si-rich particles. TEM analyses revealed that a transition in strengthening-precipitate structure occurred in the severely deformed alloy leading to a predominance of globular precipitates over the rod like phases typically found in the undeformed and aged samples. Tensile tests carried out on severely deformed and aged samples allowed to quantify the maximum strength achievable by the 6082 alloy after concurrent grain refinement and peak-hardness aging at 130C

Effect of process parameters on bead properties of A359/SiC MMCs welded by laser

Metal matrix composites are well known materials that present several positive features, mainly in terms of mechanical strength to weight ratio. On the other side, MMC’s are extremely difficult to machine (in particular by chip removal processes) and this difficulty has limited a wider diffusion. Welding, together with other joining technologies, could be a solution to limit the chip removal processes in the production of a MMC part, but this is not a problem-free process. This paper presents an experimental study on the laser welding of MMCs using both a CO2 and a diode laser source. The CO2 welding is performed in keyhole conditions (deep penetration), whereas the diode laser performs a conduction welding. Results show that the CO2 welding is greatly affected by the formation of Al4C3, that compromises the toughness of the bead. The content of Al4C3 can be reduced by acting on the process parameters, but cannot be completely eliminated. Instead, diode laser welding generates a sound bead, with negligible Al4C3 formation and of superior quality. Considering also the other positive features of this kind of sources (high efficiency and radiation wavelength, that is, highly absorbed by MMCs), diode laser welding seems to be highly recommendable for MMCs laser welding

Processing of CuZr based shape memory alloys

In the present work an investigation on primary processing of CuZr based shape memory alloys is proposed. In particular, the study addresses the effect of hot rolling process on the properties of CuZr shape memory alloys, in which the addition of some elements, such as Cr, Co and Ni, is taken into account. These alloys are produced by means of vacuum arc melting furnace under non contaminating conditions. Considering the high reactivity of these alloys, due to Zr element, hot working was undertaken after sealing the ingot cigars in a stainless steel protective can. The characterization of the rolled alloys is performed using DSC in terms of evolution of martensitic transformation temperatures. The analysis is completed with mechanical and the microstructure investigations by means of microhardness and scanning electron microscopy (SEM) observations, respectively. The main result of this work is the evaluation of hot workability property of this system, which can be improved by adding metallic elements to the binary CuZr intermetallic system. Moreover, interesting characteristics, such as high transformation temperatures, thermal stability and reduced thermal hysteresis, can be also improved by means of the addition of Ni and Co at the same time

Analisi teoriche e sperimentali sulla solidificazione di compositi a matrice di lega di alluminio

none6S. Arnaboldi; P. Bassani; M. Pini; A. Tuissi; M. Vedani; G. VimercatiS., Arnaboldi; Bassani, Paola; M., Pini; A., Tuissi; Vedani, Maurizio; Vimercati, Gianmarc

The effect of twinning and detwinning on the mechanical property of AZ31 extruded magnesium alloy during strain-path changes

In order to investigate the effect of twinning–detwinning on the mechanical properties of AZ31 extruded magnesium alloy pre-compression and pre-stretch deformation were conducted along extrusion direction (ED) at 1%, 3%, 5% strain levels. After pre-strain, the strain-path was inverted by performing tensile or compressive tests at room temperature. Results showed that the detwinning behavior occurred during the inverse tension after the pre-compression. Although due to the aforementioned effect the tensile yield strength decreased, by increasing the pre-compressive levels both fracture elongation and peak strength improved. In the inverse compressive tests after pre-stretch the {1012} twinning was restrained and the volume fraction of twins decreased, leading to the improvement of yield strength by increasing in pre-stretching levels