1,720,989 research outputs found
Le leghe alluminio-litio
Full text linkQuesto lavoro è una rassegna sintetica delle leghe Al-Li. Sono discusse le caratteristiche meccaniche (resistenza, tenacità, propagazione di cricche di fatica), inquadrate ed interpretate alla luce della composizione chimica e della microstruttura del materiale. E' esaminato anche l'effetto degli elementi alliganti introdotti nelle leghe Al-Li, che sono caratterizzate da una composizione sovente complessa. Viene anche posto e discusso il problema della saldabilità, sempre più importante per gli attuali materiali strutturali. Emerge un panorama articolato delle leghe Al-Li, delle quali alcune sono oramai prodotti commerciali consolidati, altre sono state abbandonate, altre ancora sono in fase di sviluppo o qualificazione. Complessivamente si tratta di un prodotto maturo dal punto di vista tecnologico, anche se le sue potenzialità talvolta non appaiono ancora sfruttate appien
Fatigue crack propagation in 2195-T8 aluminium alloy plate
No full textThe paper deals with fatigue crack propagation in a 2195-T8 alloy plate. It is shown that fatigue resistance of this alloy is comparable to that of the classical 2xxx or 7xxx competitor alloys. This study highlights stress ratio effects on the fatigue behaviour at the threshold: the stress intensity factor range ΔKth decreases as R increases. The crack growth path, very sensitive to the texture of the plate, occurs in a crystallographic way, giving rise to strong deflection and zig-zag advance. The crack path provokes a mixed mode I and II fatigue fracture, and makes active crack retardation by the crack closure mechanis
Application of T6 Heat Treatment on the AlSi9Cu3 (Fe) Casting Alloy and the Effect of Copper Content
Full text linkAlSi9Cu3 (Fe) foundry alloy is commonly used to produce components by High Pressure Die
Casting (HPDC) for automotive and electrical industries. Mostly for cost reasons, the Cu content is held at
the minimum of the compositional range foreseen by the standards. The strength of the metal is then quite
low and therefore the components are used only in low or non-stressed applications. The experimental results
of the present paper show that in the as cast temper, the percentage of Cu has little effect on strength. It is
suggested that alternative alloys for HPDC with lower or no Cu content be adopted for non-stressed
components. In the last 15 years, it has been demonstrated that Al-Si-Cu alloys for HPDC may successfully
heat-treated by unconventional T6 without causing surface blistering or dimensional instability. Despite the
new opportunities, there have been few industrial applications. Instead, the present authors believe possible
new technological outcomes for unconventional T6, and have therefore experimented with the AlSi9Cu3 (Fe)
alloy with different Cu contents. By using SEM-EDX microanalysis to get Cu composition maps in the alloy
microstructure, a T6 heat treatment with lower solubilization temperature and shorter soaking time to
avoiding blistering has been identified. Tensile test confirmed the effectiveness of unconventional T6 and
showed a strong increase in the elastic limit of the material. The results also show that the best effect is
obtained by increasing the Cu content as much as possible. It is therefore possible to produce components for
highly stressed structural applications in T6 treated AlSi9Cu3 (Fe) alloy
Mechanical properties of Al-based amorphous-nanocrystalline alloys
No full textThe present work deals with testing of mechanical properties of Al87Ni7Nd6 and Al88Fe9Nd3 alloys rapidly quenched in the form of ribbons, having completely and partially amorphous microstructure respectively. Al87Ni7Nd6 Amorphous alloys show three transformation events the first of which involves the formation of Al nanocrystals dispersed in the amorphous phase. The micro-hardness of samples annealed at different devitrification stages was determined. An increment in hardness from 250 HVN (as quenched samples) to 355 HVN (nanocrystalline samples) was observed. The amorphous samples were cold-rolled up to 10% elongation without formation of cracks. Shear bands were evident on the outer surface. Al88Fe9Nd3 nanocrystalline samples were cold-rolled up to 2% of elongation but cracks were detected. Tensile fracture surfaces showed dimples with diameter of the order of a hundred nanometers and no vein patterns are observed
Static and fatigue strength of a die cast aluminium alloy under different feeding conditions
No full textThis paper reports investigations of the influence of porosity and casting defects on the static and constant-amplitude fatigue strength of a die-cast aluminium alloy. Three batches of specimens, differing in the sprue-runner design and consequently in content and types of defects, were tested in 'as-cast' conditions. Defects consisted of gas and shrinkage pores as well as cold fills, dross and alumina skins. Casting defects were observed to reduce significantly the static and fatigue properties of the material. Whereas for the static characteristics the decrease was progressive with the porosity range, for the fatigue strength the decrease was most significant from the lowest to the middle porosity range. The batches were classified with regard to the porosity level, as the metallurgical defects were not detectable through X-ray examination. The content and size of metallurgical defects were observed to increase together with the porosity level. Scanning electron microscopy (SEM) observation of the fracture surfaces demonstrated the important role played by dross, alumina skins and, above all, cold fills on the fatigue fracture
- …
