Research On Welding Porosity And Mechanical Properties Of Aluminum Alloy Under Different Temperature And Humidity Conditions

In recent years, with the constant speed of the high-speed rail vehicles, thelight weight has been more and more attention. With the low density and goodmechanical properties, aluminum alloy becomes the pursuit of the main structure ofthe high-speed rail vehicles lightweight materials. However, Aluminum alloy isprone to a variety of welding problem because of strong oxidizing and easy inhaling.Among them, the stomata defect is the most prone to produce in aluminum alloymelt welding. The generation of weld porosity has a great relationship with thewelding environment. Through my own design and production of the atmosphericenvironment simulation system, this project research the influence law of differenttemperature and humidity conditions on welding blow hole defects, and the defectsof porosity on the mechanical properties.This paper designs and manufactures the temperature and humidity simulationenvironment system by myself, which can preset and control temperature andhumidity of the welding environmental. Furthermore, this paper designs automaticwelding system which can match the simulated environment system. We can controland operate the process of automatic MIG welding on aluminum alloy test plate inoutdoor environment, and observe the process in indoor environment through thereserved seal window.The welding parameters which can get the good welding seam have beendetermined through the experiment. The welding experiment has been proceeded infive humidity conditions which have been selected in5℃and22℃respectively,and research the influence law of different temperature and humidity conditions onwelding blow hole defects. With the explanation of the relationship between therelative humidity and the absolute humidity, the influences of different temperatureand humidity conditions have been analyzed comprehensively. The results showthat the quantity of welding stomata increases with the increase of environmentalhumidity. Then this paper research the influence of welding stomata on the staticsand fatigue performance with the welding test plates which contain differentporosities. Fracture morphology characteristics and the influence of fracture havebeen analyzed though the morphology observation of static load fracture andfatigue fracture by using SEM. The results of fracture scanning expound the static load fracture all contains the dimple, and the crack source area of fatigue fracturesurface exist welding defects such as pores and inclusions, which has very bigeffect on fatigue performance of welding joint.Furthermore, this paper has established the finite element model with weldingstomata defects, and introduced the thermal elastic-plastic model with the strainhardening. Then the residual stress and mechanical properties of welding structurehas been researched though the nonlinear finite element simulation software namedMSC.MARC, which purpose is to study the influence of welding blow hole defecton residual stress and mechanical properties. As a result, the finite elementsimulation and experimental results are in agreement.