The present paper investigates some mechanisms of modification the eutectic of aluminum-Silicon (Al-Si) alloys. These alloys have been many applications in general industries especially in military, aerospace and automobiles. These alloys in some cases need to modify their properties In particular the wear resistance. This can be overcome by modification the morphology of Si-eutectic. Many mechanisms were suggested in this field. The most common mechanisms are chemical modification and quenching modification. The chemical modification achieved by adding some rare earth elements like sodium (Na), strontium (Sr), and antimony (Sb). Also can be refined the structure of these alloys by using master alloys such as Al-Ti, Al-Ti-B and Al-B. According to restricted growth theory, the impurity induced twinning which reduce the growth. According to the restricted nucleation, the twin plane re-entrant edge (TPRE) Poisoning, which stopped the twin plane. The addition of sodium (Na) in the range of 0.005 to 0.01% modifies the eutectic Si but it has high vapourity and it is difficult to determine its resulting level. Strontium is added in a range of 0.02 to 0.04% but it is ability to oxidation is high as contact with atmosphere.
Aluminium Alloy AA7075 is the strongest heat-treatable aluminium series. For that they have suitable properties and tremendous applications, especially in the aviation and aerospace industries. The effect of a minor Nanocobalt oxide on the microstructures and mechanical properties of AA7075 was investigated in this work.The investigation was carried out as a cast AA7075 with 0.2, 0.4, 0.6 and 0.8% Nano-cobalt. The optical microscopy demonstrates that the grain size of alloys was decreased with the increasing of Nano -cobalt oxide content.
The Scanning electron microscopy and EDX show that the cobalt oxide present between the grains at the grain boundary. Moreover, there are Al-Zn-Mg, Al-Fe-Cu, Si-Al-Zn, Al-Fe-Cu-Co-Zn, and Al-o-Si-Zn-Cu compounds.The mechanical properties examination shows that the hardness decreased and yield stress, increased with an increasing in the Nano-cobalt content. The ultimate tensile stress and modulus elasticity also increased with the increase of Nanocobalt content, except alloy with 0.8% Nano-cobalt which decreased to 5.87 GPA.
Carbon steel was coated with Cr-multi-walled carbon nanotube (MWCNTs) coatings via electrodeposition. In this article, the impact of a combination of MWCNTs into the chromium coating on the morphology of the coating surface and corrosion characteristics was inspected. The MWCNTs seem to be evenly distributed across the chromium layer, according to scanning electron microscopy (SEM). Electrochemical measurements were used to conduct corrosion tests on samples of MWCNTs– chromium composite coated and pure chromium coated samples in aqueous NaCl (3.5 wt.%). The outcomes demonstrated a considerable increase in the resistance of corrosion due to the inclusion of MWCNTs during the chromium deposition procedure. In addition, the mechanism of anti-corrosion of the composite coating is also presented. Using an electrolyte bath containing various concentrations of dispersed MWCNTs (0.5, 1, and 1.5 g/L), crack-free and compact coating of Cr-MWCNT composite were electrodeposited on the substrates of the mild steel. The potentiodynamic polarization technique was used to examine the coatings corrosion performance subjected to a 3.5 weight percent of NaCl medium. When compared to chromium coating, the Cr-MWCNT composite coating showed the lowest corrosion rate (1.045x108 mpy) compared to chromium coating (4.891x108 mpy).
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