Diffusion in aluminium alloys, Hot deformation (rolling) of aluminium Dissertation

Diffusion in aluminium alloys, Hot deformation (rolling) of aluminium alloys and its dynamic recovery, dynamic recrystallisation - Dissertation Example The activation energy and diffusion constants are calculated using a variety of factors like the solid solubility, alloying content and the state of the matrix microstructure in terms of grain boundary size, dislocation density and vacancy concentration [PAPM]. The mean distance travelled by the atom during diffusion in turn is dependent on the rate of diffusion D as follows: L = (Dt)? Where L = the mean distance travelled by the atom. t = time (s) All atoms above absolute zero (-273oC) vibrate and the frequency of vibrations acts as the driving force for the movement of the atoms or for their diffusion. The frequency of vibration and diffusion increases with the rise in temperature. However, for atoms to be able to move from one lattice point to the other, the atoms need to overcome the activation energy. This activation energy is low around the metal surface and at the grain boundaries, and this is the reason for the high concentration of the precipitating solute at the grain bound aries. ... Also, temperature has a greater effect on the diffusion distance compared to time as increasing the temperature increases both the number of vacancies in a metal as well as the energy of the diffusing atoms (Wolverton, 2007). Thus, in an increased temperature, atoms are able to diffuse faster and farther. The rate of diffusion differs for atoms of different alloys and hence the reduction of micro-segregation with homogenization differs for different alloys due to the difference in their compositions. As seen from the diffusion equations presented above, the distance that atoms need to travel (which depends on the dendrite arm spacing, the relative abundance of atoms) impact on the time and temperature needed to attain the desired level of diffusion for reduction of micro-segregation. Figure1: Relative homogenization times for given dendrite cell sizes and temperatures in common aluminum alloys. (Source: Chakrabarti, 2001) According to Verlinden et al [1990] found that the dissolution of theta and S particles in an as-cast 2024 billet during a homogenization at 460oC was not possible even after 24 hours. The volume fraction was found to decrease with time but with an associated coarsening of the remaining S and theta particles resulting in coarser particles than when in the as-cast condition. A homogenization temperature of 500oC was found to completely eliminate both the S and theta particles. Due to the distances that diffusing solute atoms travel during practical homogenization treatments, these treatments are effective at removing microsegregation effects but may have little impact on macrosegregation. 2.2 Theory related to Hot Deformation Hot rolling is the

Strategic Management and Leadership Assignment Example | Topics and Well Written Essays - 3500 words - 1

Strategic Management and Leadership - Assignment Example Its range of products include; camera lenses, cameras, microscopes, binoculars, ophthalmic lenses, steppers and measurement instruments (Suzuki et al., 2000). During the 3rd quarter ended in December 31, 2014, the company’s total assets increased by 48, 560 million yen from the past fiscal year to 998,075 million yen. This can be attributed to the increased cash and deposits approximated at 9,827 million yen, inventories by 27,113 million yen, and accounts receivable by 11,056 million yen. On the other hand, total liabilities increased by 20,745 million yen from the previous fiscal year to the 423,448 million yen. This was attributed to the increased accounts payable and notes by 15,106 million yen (Nikon, 2015). Comparing the increased total assets and liabilities, it’s evident that total increase in assets was more than the total increase in liabilities signaling a positive growth for the company. In third quarter of the year ending March 31, 2015, the precision equipment business posted a substantial decline in the income for the Q3 and the three quarters total year on year owing to the decline in sales. Similarly, the imaging products business income and sales decreased for the Q3 and three quarters total year on year. However, the overseas sales in the microscope solutions business increased. As of 31st march, 2015, the company’s net income was 46,824.0 million yens reflecting an increase of 4,365 million yens as compared to the previous year (Nikon, 2015). The increased income reflects the company’s success. The expansion of the company to reach out to seven continents is an indication of not only the increased market share for the company but also indicates how the company has been successful. It’s clear that without success the company could not be able to expand to the seven major continents. This can be