ABSTRACTA
Temperature of aluminium alloy is simulated using MATLAB programming language for annealing, soaking to have uniformity of microstructure and quenching treatment processes. Workpiece selected for the study was aluminum alloy 6061-O, T1, T4 and T6 of different shapes: plate, cylindrical, rectangular, cubic and spherical aluminum alloy. The simulation identified the following properties: geometry (size), thermal conductivity, density, load pattern or shape which determine possibility of good heat treatment. Temperature of treated specimen were analysed using Finite Difference Method. At annealing temperature of 409.5 oC, fracture resistance of 670.5MPa and ultimate tensile strength value 298 MPa were achieved with 4% of ductility. Holding this temperature of 409.5 oC was necessary for achieving uniform microstructure at about 600 seconds which later quenched in water for 799 seconds to room temperature of 28 oC. Therefore the aluminum has equivalent length (thickness) treated of 25mm in plate section. The workpiece in the study increases in strength with increase in temperature for annealing therefore increases in thermal conductivity of the specimen was experienced. However, heat treatment in plate section of aluminium (6061-O) was faster in comparing to rectangular and cylindrical surfaces. Heat transfer coefficient was 1384W/m2K in plate and 692 W/m2K in cylindrical specimen of Biot number 0.2. The heat treatment processing was completed after 2256 seconds and aluminium 6061-O is more easily heat treatable to aluminium 6061- (T1, T4, T6) under the same condition. However, annealing of aluminium 6061 would negate effect of cold working at strain of 0.002 with yield strength of 149 MPa at ductility of 0.2%.
CHAPTER ONE
1.0 INTRODUCTION
1.1 Background of the Study
Planning and scheduling could be explained as a process that involves taking decision which is mostly used on a continuous basis in manufacturing and service industries. These kinds of decision-making play a vital role in production and procurement, in distribution and transportation, and in communication and information processing and among others (Pinedo, Glynn, et al., 2005).
In heat treatment planning process, decision making method which tends to improves Aluminium Alloy samples of geometry functionability is very necessary. Basically, this process is usually used to alter the physical, and sometimes chemical, properties of the material. Also heat treatments could be used for the production with several related materials, such as glass. The process heat treatment entails heating of material to high temperatures, to obtain a desirable outcome such as softening or hardening of the material. The methods used in carrying out the process include case hardening, precipitation strengthening, annealing, tempering and quenching. Therefore heat treatment deals with condition in which heating and cooling are carried out for a particular reason of changing the properties of materials. However, the process of heating and cooling are sometimes form incidentally in the manufacturing processes which includes welding or hot forming. These processes is usually considerably practice to obtain increasing the strength of material, improve machining, and induces formability and restoring ductility with respect to cold working operation. Heat treatment has contributed immensely to manufacturing industries by improving the quality and the mechanical properties of materials which are to be manufactured.
1.2 Justification and Significance of the Study
Heat treatment is usually carried out to strengthen workpiece and also to improve manufacturability function during forming or machining. The quality of heat treatment for aluminium alloy workpiece depends on mechanical property and furnace temperature. It is good to determine the heating history and temperature distributions at different point in furnace and in workpiece. This will definitely improved the material loading design and temperature control. Unfortunately, there is presently no elaborate technique in place to simulate the process of heat-treatment. The present practice in heat treating industry ensures quality by experimental methods by measuring the temperature distribution in the furnace space or on the material surfaces.
Heat treating processes have faced difficulties in measuring temperature differences of a workpiece temperature because most methods available were indirect.
From the outside to the interior of the workpiece, the temperature is usually varied with respect to time and location. However, thermocouple is usually used to measured workpiece temperature which is set on the workpiece surface at selected points while the temperature inside the workpiece is unknown. Here, to obtain homogenous temperature distribution, a delay in time is very important in which through conduction that will be achieved. The major challenge is that there is no analytical model established for the time factor which is basically based on experience. With this constrain in either cases (wheather time is relatively too short or too long), it will have effect on the heat treated product, thus affect the functionality of the product. Also, there is no analytical model that could be used in determine the loading design of aluminium alloy workpiece. This made it difficult to establish an optimisation of the material loading due to non uniformity of temperature distribution experience in the workpiece. The need to developed AAW mathematical model for heat transfer in the process cannot be over emphasized. This could be achieved and modelled using the principle of conduction as well as finite difference method for predicting temperature history of AAW.
Aluminium alloy workpiece could be used to heat treatment relieve internal stresses, to improve machinability and thus reduce brittleness. The mechanical Properties of AAW which includes toughness, hardness, strength, wear resistance, etc can be altered to achieve particular applications. Generally, the fundamental principle of heat treatment of AAW is the process of heating and cooling thereof.
Heating and slowly cooling will relieve internal stresses in most materials. Therefore, the underlying micro-structural changes induced in materials during heat treatment are complex. In the aerospace industry, heat treatment is usually performed after welding or forming (Alberg, 2003).
The use of computer program to simulate and predict temperature history of AAW during heat treatment would help to predict functionability of the material in a given time at optimised cost.
1.3 Aim and Objectives of the Study
Aim
This study aimed at developing a computer program for predicting temperature history during heat treatment of AAW. The objectives of the study include to:
Objectives
i. predict annealing temperature
ii. predict soaking temperature
iii. predict quenching temperature
iv. investigate the rate of heat transfer in the workpiece using Biot number
v. investigate the hardness of the material
1.4 Scope of this Study
This study is model and simulates heat treatment cycle consisting of annealing process, soaking (holding) and quenching (cooling) that may be used for Aluminium alloy samples of various geometrical sizes. The model makes use of finite difference method to numerically distribute the temperature profile in the workpiece. Similarly Brinell hardness test was conducted experimentally to validate the obtained result.
This material content is developed to serve as a GUIDE for students to conduct academic research
COMPUTER SIMULATION OF HEAT TREATMENT PROCESS FOR ALUMINIUM ALLOY
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