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Formability of Wrought Magnesium Alloys by Hot Compression Testing and Laboratory-Scale Extrusion
No full textThe present study is aimed at investigating the high-temperature behaviour of commercially available alloys under conditions of interest for their extrusion. The AZ31B and ZM21 alloys were studied by hot compression testing in the temperature range 320-450°C (selecting four different levels for each alloy, depending on its composition) and at four values of initial strain rates, lying in the range 5.56•10-4 s-1 -2.78•10-2 s-1. A laboratory-scale extrusion rig was also adopted to produce extrudates in the form of bars and hollow tubes (external diameters from 8 down to 4 mm) according to the optimized parameters defined by the hot compression tests. Microstructural analyses were carried out to deeply investigate the evolution of microstructure during extrusion and to draw comparisons among hot compressed and extruded samples
Processing of wrought magnesium alloys to produce small tubes for biomedical applications: investigation about the extrusion process by a laboratory test rig
No full textTwo commercial ZM21 and AZ31B alloys were extruded into small-size tubes at 410°C and strain rate 2.78•10-3 s-1 by a laboratory hot-extrusion system. The series of tubes, with outer diameter in the range of 8-4 mm and inner diameter from 6 to 3 mm were investigated considering microstructure and texture analysis. The tubes featured a homogeneous and refined equiaxed grain structure since dynamic recrystallization was clearly observed during the extrusion process. A typical ‘basal’ type texture was detected in extruded tubes by using EBSD technique
Formation of small-siza tubes and material characterization for biodegradable magnesium stent precursors
No full text
Tecniche di analisi del comportamento meccanico di rivestimenti e strati superficiali
No full textla memoria illustra alcune tecniche di caratterizzazione della resistenza meccanica, delle proprietà
elastiche e del comportamento ad usura di rivestimenti e strati superficiali prodotti su componenti
metallici. Attraverso l’esposizione di risultati riferiti a ricerche su rivestimenti ottenuti con diversi
tipi di trattamento, si illustrano tecniche di analisi meccanica quali le prove di deformazione con
sensori di emissione acustica, le prove di scratch, quelle ad usura mediante tribometri e le prove di
indentazione strumentata, che vanno naturalmente abbinate ad analisi microstrutturali e di
composizione chimica per una corretta previsione delle prestazioni degli strati superficiali di un
componente meccanico
Ultra-fine grained degradable magnesium for biomedical applications
No full textProperties of commercially available purity magnesium and wrought ZM21 Mg alloy were investigated in view of their
biodegradable applications. In particular, the opportunities offered by grain size refinement down to the ultra-fine scale achieved by
equal channel angular pressing (ECAP) and warm extrusion were discussed and material properties were analyzed. Results show that
the grain refinement will lead to a significant improvement in compression strength. The tension strength of the coarse grained alloy
is always significantly higher than that measured in compression due to the sharp texture of the starting wrought alloy. ECAP also
causes an attenuation of the above texture effects, promoting marked changes in plastic flow behavior. The corrosion behavior of the
investigated materials are affected by a combination of microstructural effects such as chemistry, grain size and the extent of lattice
distortion inherited from previous processing stages. ECAP leads to refinement of grain size and to increased lattice defect density
which apparently produce counterbalancing effects on corrosion performance. The improved dispersion of second-phase particles
brings positive effects on development of pitting
Extrusion of Magnesium Tubes for Biodegradable Stent Precursors
No full textProduction of stent precursors in the form of small-size tubes has been evaluated by hot compression tests and extrusion trials on the
5 AZ31B and ZM21 magnesium alloys. The investigation here presented mainly reports on the effects of extrusion parameters on microstructure
and properties of the tubes. Processing at 410C and at slow strain rate (2.78 103 s1) by a laboratory hot-extrusion system allowed
producing small-size tubes featuring a homogeneous and refined equiaxed grain structure. Microstructural analyses showed that dynamic
recrystallization, often anticipated by deformation twinning, took place during hot forming. By a proper control of extrusion parameters,
tubes with wall thickness as low as 0.5mm could be successfully produced
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