Dissertation > Excellent graduate degree dissertation topics show

Study on the Plane Strain Fracture Toughness of AZ31B Magnesium Alloy and Its Welded Joints

Author: XieRui
Tutor: WangWenXian
School: Taiyuan University of Technology
Course: Materials Processing Engineering
Keywords: Magnesium alloy Welded joints Fracture Toughness Three-point bending Fracture analysis
CLC: TG407
Type: Master's thesis
Year: 2010
Downloads: 108
Quote: 0
Read: Download Dissertation

Abstract

High strength magnesium alloy lightweight and easy to recycle a series of advantages, its research and application of more and more the world materials academia and industry concern, known as the 21st century the most potential for development and the future of green engineering material. Magnesium alloy has become the third largest engineering materials after following the steel and aluminum. However, if widely used as a structural member, magnesium alloy must face connectivity problems. The welding is a preferred method of connecting. The plane strain fracture toughness KIC for the characterization of materials to resist crack instability scalability material constants, one of the basic parameters is essential to measure the material properties of modern engineering design. Because of the fracture toughness of the welded joints are important factors to affect the security of the welded structure, magnesium alloy and its welded joints of KIC pilot study. In this paper, the three-point bending (SEB) method tests AZ31B magnesium alloy and welded joints of the plane strain fracture toughness test. The paper focuses on testing AZ31B magnesium alloy base metal of AZ31B magnesium alloy tungsten inert gas (TIG) central area of ??the weld, the weld heat affected zone and longitudinal joints (cracks across the weld) specimen load - crack mouth opening displacement ( PV) curves were calculated on this basis, their plane strain fracture toughness KIC values. Their microscopic and macroscopic fracture morphology were analyzed and compared, the test also give special consideration to the factors of the extrusion direction of the plane strain fracture toughness value. Pair of notches direction parallel to the extrusion direction, and a 45 ° oblique and vertical AZ31B magnesium alloy base material SEB specimen three-point bending test, the load - the crack mouth opening displacement (PV) curves and calculated their KIC values. Fracture toughness range wherein the gap direction parallel to the extrusion direction of the test piece to 8.94MPa m ~~ of 10.13MPa m, the gap direction 45 ° inclined to the extrusion direction of the test piece fracture toughness range 9.06MPa m ~ 10.15MPa m, notched direction perpendicular to the extrusion direction the range of fracture toughness test pieces of 8.91MPa m ~ 11.71MPa m. Three-point bending test, respectively, of the central area of ??AZ31B magnesium alloy welds and heat affected zone SEB specimen measured PV curve calculated plane strain fracture toughness KIC range were 15.75MPa m ~ 18.47MPa m and 12.89MPa m ~ 14.67MPa m. Three-point bending test measured the PV curve calculated plane strain fracture toughness KIC range was 15.74 for each specimen group KIC value of the longitudinal weld AZ31B magnesium alloy (crack across the weld) SEB specimen comparative analysis, the general performance of resistance to crack propagation ability of the merits of the order as follows: of AZ31B magnesium alloy welds the central area of ??the specimen, the longitudinal weld, the weld heat affected zone gap vertical extrusion direction of the base metal specimen notch tilt squeeze base material specimens in direction of 45 °, and the gap parallel to the extrusion direction of the base material of the test piece. Using a scanning electron microscope (SEM) for each group specimens fracture since crack at the start to the end was observed, the results showed that the overall performance of the most fracture gradually enhanced cleavage fracture morphology. The individual fracture appears to have a small amount of fatigue stripes, this is due to the a preset fatigue crack complex internal stress and the joint action of external stress generated in the center of the weld and the AZ31B magnesium alloy and its welded joints calculated plane strain fracture toughness KIC values ??are smaller, the cleavage fracture morphology observed consistent. Found that in addition to the gap parallel to the extrusion direction of the base metal specimen fracture is more flush with almost no deformation, the remaining test items macroscopic fracture significantly deformed by observation and analysis of macro-photographs of each specimen fracture, especially in direction on both sides of the position of the specimen thickness of about 3mm Yamagata tear ridge. And the plastic deformation of the size of its plane strain fracture toughness KIC value of size are positively correlated.

Related Dissertations

CLC: > Industrial Technology > Metallurgy and Metal Craft > Welding, metal cutting and metal bonding > Welding general issues > Mechanical properties of welded joints and Intensity
© 2012 www.DissertationTopic.Net Mobile