1、 PDF外文：http:/ 关于工艺参数对热挤压镁合金影响的研究 1 Investigation of the influence of process parameters on hot extrusion of magnesium alloy tubes Abstract: During the hot extrusion of magnesium alloy, the change of process parameters will affect the mechanical properties of extruded product
2、s. In this study, Taguchi method and analysis of variance (ANOVA) are applied to analyze the influence of process parameters on the hot extrusion of magnesium alloy tubes under extrusion ratio of 21.05. The experiments are arranged by orthogonal array method in which magnesium alloys AZ31and AZ61 ar
3、e used as outer arrays, the factors selected as inner arrays are the billet heating temperature, the initial extrusion speed, the container temperature and the lubricants. The extruded tubes will be carried out tensile test and flattening test, the test results are analyzed by the quality measuremen
4、t of Taguchi method to find the relationship between the process parameters and mechanical properties of the products, and to acquire the optimal combination of parameters. Then based on the results obtained from the additive model, confirmatory experiments are performed. Besides, the microstructure
5、s of extruded tubes are observed to clarify the influence of process parameters on the grain size. Finally, with the same extrusion condition, the variations in tensile strength and flattening strength due to different compositions are discussed. 2007 Elsevier B.V. All rights reserved. Keywords: Hot
6、 extrusion tube； Magnesium alloy； Mechanical properties； Taguchi method； Orthogonal array 1. Introduction Magnesium alloy has low specific gravity, high specific strength, good ventilation and shock absorption. It is also opaque to electromagnetic waves and recycle. In recent years, magnesium alloy
7、has begun to replace steel, aluminum and plastic as products have become increasingly miniaturized. Magnesium alloy is 35% and 77% less dense than aluminum alloy and steel, respectively. Therefore, as lightweight products, environmental protection and recyclability become increasingly important, the
8、 demand for magnesium alloy has increased and been extensively applied to the automobile industry, the bicycle industry, the aerospace and national defense industries, the civic product manufacturing industry and the 3C (computer, communication and consumer electronic) electronic industry. At presen
9、t, die casting is the main method for forming and processing magnesium alloy.Wu and Chang used the Taguchi method in the die casting of magnesium alloy to produce a cover for a personal data assistant (PDA), and thus to identify the optimal process parameters. Takudaetal adopted the finite element m
10、ethod to analyze the formability of AZ31 magnesium base material during deep drawing. Finite 关于工艺参数对热挤压镁合金影响的研究 2 element analysis can be used to predict cracking position, which can then be verified experimentally. Chen et al.applied an AZ31 magnesium alloy sheet to study t
11、he deep drawing of a square cup. Following deep drawing at room temperature, the final sheet had defects, but at over 200 C, the formability is improved. In a related study of magnesium alloy, Mwembelaetal.studied the microstructure of AZ31 magnesium alloy during hot working.A high temperature of 30
12、0450C was firstly employedfor rolling, which was followed by forging. As the temperature increased over 300C, the grains grew, and the strength of the alloy decreased. In a study of the extrusion of magnesium alloy, Gouveiaetal. used the finite-element method to simulate forming by cold forward extr
13、usion. Chandrasekara and Shyan John investigated three magnesium alloys, AZ31, AZ61 and ZK60, as well as the effect of temperature on formability during forward extrusion. They showed that these magnesium alloys cannot be formed at between room temperature and 175 C, and that these magnesium alloys
14、can be extruded smoothly at 200 C, but AZ31 and ZK60 magnesium alloys exhibit cracking. When the temperature was increased to 300 C, the AZ31 magnesium alloy could be well formed. Mural et al. empolyed AZ31B magnesium alloy billets formed by casting, as well as homogenized materials to perform extru
15、sion. The microstructure and mechanical properties of the final products were then studied. Using the Taguchi method for plastic processing does not reduce the accuracy of the experimental results, but significantly reduces the number of times the experiments must be performed. It is therefore regar
16、ded as a more effective study method. In this study, two magnesium alloy billets, AZ31 and AZ61,are applied to carry out hot extrusion into a tube with a thickness of 2 mm. The Taguchi method is initially applied in the experimental planning and the process parameters of hot extrusion are set to opt
17、imize the mechanical properties for AZ31 and AZ61 tube. ANOVA is then employed to analyze the effect of the process parameter on the tube. Finally, the effects of the initial extrusion speed and the lubricant on the mechanical properties of the tube are investigated. 2. The principles of quality des
18、ign Taguchi method The experiments can be planned in four ways: (1) trial-and-error；(2) one-factor-at-a-time experiments； (3) full-factorial experiments； and (4) Taguchis orthogonal arrays (OA).Orthogonal arrays can eliminate the bias produced by one-factor-at-a-time experiments, and improve the exp
19、erimental efficiency of full-factorial experiments. Based on the principle of maintaining the accuracy of experiment results, the use of orthogonal arrays can considerably reduce the time required to perform the experiments, and increases the reproducibility of the experiment results. This method ca
20、n also be employed to optimize the process parameters. Therefore, orthogonal arrays are applied herein to perform experimental planning. 2.1. Experimental planning method The Taguchi method uses the signal-to-noise ratio (S/N) as a quality benchmark, 关于工艺参数对热挤压镁合金影响的研究 3 bas
21、ed on the ideal function, different measures are used for the various quality properties. S/N ratios are one of the three forms the normal-the-best, the smaller-the-better and the larger-the-better. The mechanical property discussed herein is tensile strength. It is the larger-the-better characteris
22、tic. Therefore, an S/N ratio that is the larger-the-better is used, and is given in Eq. (1). (1) in the equation, n stands the total number of measurements, and yi the measured quality value. The i in the suffix refers to the number of the experiment in the plan based on orthogonal arrays, and
23、 the calculated S/N ratio is used in the factor response statistical analysis, and the optimal combination of process parameters can be obtained. 2.2. Application of analysis of variance The statistical analysis of variance (ANOVA), used in the Taguchi method, is adopted mainly to evaluate the signi
24、ficance level of experimental errors and every factor response. The equations used in the ANOVA statistical analysis in this study are as follows. (1) Sum of squares of the factor effect vector, SSfactor (2) where n is the number of times the experiment is performed, r is the num
25、ber of times the experiment is repeated, L is the number of factor levels, yk is the response value of that factor at level k, and ym is the average of all experimental data. (2) Sum of squares of the total variation vector, SStotal (3) where yij stands for the j experiment data of the
26、 its set of experiment. (3) Error sums of squares, SSe SSe = SStotal SSfactor (4) (4) Degree of freedom of the factor effect vector, DOFfactor DOFfactor = L 1 &n
27、bsp; (5) (5) Degree of freedom of the total variation vector noises, DOfactor DOfactor = n r 1 (6) (6) Variance of the factor, Vi iii DOFSSV (7) (7) Distribution of the predicted values of the two variances, F Verrorfactorfactor VF (8)
