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The most important commercial casting alloys are those based on Al–Si. Their technical characteristics are highly connected to their as-cast microstructure, which is translated by the secondary dendrite arm spacing (SDAS). The alloy microstructure has been demonstrated to be changed by the adding of certain alloying elements, in the sense of boosting the desired properties and features. Search has been intensified to provide a positive balance of several properties, such as: high yield strength, high electrical conductivity, and high corrosion resistance, besides maintaining the ability for the alloy to be conventionally solidified. Under such context, both addition of Ag and the control of the fineness of the dendritic structure can be alternatives seeking better properties for Al–Si alloys. In addition to the possibility of application in current studies contributing to the growing development needs as engine materials, Al–Si–Ag alloys can emerge as an alternative to the manufacture of parts for electric vehicles, such as rotors and inverters, where high mechanical strength, corrosion resistance and electrical conductivity are required. Corrosion findings of Al–Si–Ag specimens having quite different SDAS of five alloys are presented here: Al-5wt.% Si, Al-5wt.% Si-0.1wt.% Ag, Al-10wt.% Si-0.1wt.% Ag, Al-5wt.% Si-2wt.% Ag, Al-10wt.%Si-2wt.%Ag alloys. A complete set of characterization with potentiodynamic polarization, electrochemical impedance spectroscopy, immersion tests, optical microscopy and scanning electron microscopy (SEM) was developed for these alloys. It has been demonstrated that increase in the alloy Si content diminishes corrosion resistance, and that increase in Ag content, considering Al-10% Si alloys, reduces corrosion resistance as well, despite creating thicker passive films. Furthermore, the alloys with the lowest Ag content (0.1 wt.%) had the greatest corrosion performance among the Ag-containing alloys, while the microstructure refinement tends to enhance the nobility of the samples.

The aim of this study concerns the effect of multi-pass shielded metal arc welding (SMAW) on the corrosion behavior of CW6MC cast nickel alloy. Using optical and SEM techniques the welded joint is analyzed. Vickers microhardness mapping and potentiodynamic polarization in NaCl and H2SO4 solutions are also evaluated. Both the Laves phase and NbC-type carbides are identified in the base metal (BM) and weld metal (WM) regions. The main microstructural difference observed between these regions is the morphology aspect and fineness of the dendritic arrays. The welding process promotes the finer columnar grains formation with refined intermetallic particles in the WM than equiaxed grains of the BM, which in turn results in higher microhardness values in the former region. However, no substantial changes were observed in the corrosion behavior between the BM and WM regions, considering both acid and saline media. Nevertheless, during the multi-pass SMAW process, some non-metallic micrometric inclusions (Mo and S-rich regions) can be constituted to occur in the WM region. This is associated with a significant drop in the corrosion performance of this region when the electrochemical tests are evaluated.

Abstract Shrimp shells are a raw material rich in chitin, a precursor of chitosan biopolymer. The variables of processing (demineralization, deproteination and deacetylation) can be manipulated to determine the main characteristics of chitosan, the degree of deacetylation (DD), and average molar mass. This study evaluated the influence of one of the unit operations of shrimp shell physical processing, the milling, on the final product characteristic, chitosan. After different milling conditions, the raw material was subjected to standard chemical processing for chitin extraction, followed by deacetylation to obtain chitosan, which is characterized by 1H NMR, SEM, XRD, N2 physisorption (BET) and viscometry. The results indicated that the milling time of the raw material can be manipulated to increase the material depolymerization, significantly influencing the molecular weight reduction of chitosan a desirable feature for many applications of this biopolymer, and usually obtained by complex chemical and enzymatic methods.