Mechanical behavior of A356 matrix nanocomposites fabricated using two step mixing via stir casting technique
In this work an investigation of compressive strength and forgeability behavior have been made to explore the effect of SiC nano particles on A356 alloy matrix for the development of A356/SiC nanocomposites using two step mixing through stir casting technique. A356 alloy ingot was selected as a matrix and AFP+SiCn (99.9% pure aluminium fine powder+nano size SiC mechanically forged by using ball mill at 100 rpm for duration of 10 hours) as a reinforcement. Argon gas was used to protect from oxidation during ball milling process. SiC nano particles were varied from 1% to 5% in a step of 1% by weight. In stir casting technique, stirring process was performed at 500±50 rpm for mixing AFP+SiCn in the melt matrix for total stirring period of 10 minutes in two steps. Composites were poured at 680±20° C into the permanent mould. Compressive strength and forgeability tests of fabricated nanocomposites were evaluated by using hydraulic pellet press machine. To analyze the fractured mechanism SEM microstructure was examined. The presence of SiC nano particles were confirmed by EDX spectrum. It was revealed from the results that compressive strength increases with increment of SiC nano particles and found as 603 MPa at 5% SiC nano particles. Whereas forgeability of the nanocomposites were decreased with the increment of SiC nano particles. SEM micrographs showed the ductile fractured mechanism was dominant over the brittle fracture. The main constituents present in the nanocomposites were verified by EDX spectrum.
Fabrication of nano-sized Al2O3 reinforced casting aluminum composite focusing on preparation process of reinforcement powders and evaluation of its properties
In this study, a novel approach was used to fabricate Al2O3 nanoparticle reinforced aluminum composites to avoid agglomeration of nanoparticles in matrix. Al2O3 nanoparticles were separately milled with aluminum and copper powders at different milling durations and incorporated into A356 alloy via stir casting method. The effects of milling process and milling time on mechanical properties of the composites were evaluated by hardness, tensile, and compression tests. Based on the results, some of the composites, reinforced with Al2O3-metallic mixed powders, showed higher mechanical performance compared with that of the pure Al2O3 nanoparticle reinforced composite. This enhancement is related to uniform distribution of individual nanoparticles and grain refinement of A356 matrix, shown in microstructural studies. Moreover, the results showed that an increase in milling time, led to a gradual decrease in mechanical performance of the samples. It can be related to further oxidation of metallic powders that can act as inclusions and also further probable contamination of nanoparticles with increase in milling time. Studies on the fracture surfaces revealed that the failure of matrix was the basic mechanism of fracture in the composites. Agglomerated nanoparticles were observed on dendrites in the fracture surface of the Al2O3–Al reinforcement samples.
American Insurgents, American Patriots: The Revolution of the People
This is a story of rumour, charity, vengeance, and restraint. "American Insurgents, American Patriots" reminds us that revolutions are violent events. They provoke passion and rage, a willingness to use violence to achieve political ends, a deep sense of betrayal, and a strong religious conviction that God expects an oppressed people to defend their rights. The American Revolution was no exception. A few celebrated figures in the Continental Congress do not make for a revolution. It requires tens of thousands of ordinary men and women willing to sacrifice, kill, and be killed. Breen not only tells the history of these ordinary Americans but, drawing upon a wealth of rarely seen documents, restores their primacy to America's road to independence. Mobilizing two years before the Declaration of Independence, American insurgents in all thirteen colonies concluded that resistance to British oppression required organized violence against the state. They channeled popular rage through elected committees of safety and observation, which before 1776 were the heart of American resistance. "American Insurgents, American Patriots" is the stunning account of their insurgency, without which there would have been no independent republic as we know it.