Research On Galvanic Corrosion Of Aluminum Alloy And Titaniμm Alloy

In nowadays, the aircraft plays an increasingly important roal in people’s daily lives. The structural materials of aircraft directly determines its performance. TC18titanium alloy is a new type of α+β two phases high strength titanium alloy which is developed by Former Soviet Union. Its nominal composition is Ti-5Al-5Mo-5V-1Cr-1Fe. It can be widely used in structural components.7050aluminum alloy and7475aluminum alloy is belonge to Al-Zn-Mg-Cu alloy series. As the main part of aluminum alloy with high strength and high toughness, they are widely used in many of the important parts of the plane because of their many advantages such as:high strength, hardness, durability, good corrosion, high toughness TC18titanium alloy, with positive potential, can result in serious galvanic corrosion of other materials when contacts with other materials in the corrosive environment, this galvanic corrosion will be a serious threat to the security of airplane. Therefore, it has important pratical significance to research contact corrosion and protection of TC18titanium alloy and aluminum alloy in marine atmospheric environment, which will provide theoretical basis for meterials’ matching.The galvanic corrosion of aluminum alloy with different surface treatment and TC18titanium alloy which have been exposed respectively in marine atmospheric environment of Hainan and Qingdao for two year is been studied in this paper. The exposure samples and non-exposure samples of7050aluminum alloy and7475aluminum alloy have been processed by tensile and fatigue performance test. Then, use the T statistical to analysis the marine atmospheric corrosion whether has significant difference for the test datum. Then using F test to analysis the test factors whether have influence of samples’ mechanical properties which exposured in marine atmospheric. And the comprehensive utilization of metallographic microscope, scanning electron microscope, energy spectrum are used to analyze the influence of aluminum alloy’s mechanical properties from the microstructure, surface corrosion morphology, corrosion degree, fracture morphology, second phase composition and composition of corrosion product. As well as the aluminum alloy fracture mechanism. The results as follows:After2years exposured, the aluminum alloy with different surface treatment were pitting phenomenon; The contact corrosion grade of boric sulfuric acid anodizing were2. The contact corrosion grade of boric sulfuric acid anodizing after painting were0. The boron sulfuric acid anodizing and painting can prevent the pitting corrosion of aluminum alloys and contact corrosion in a certain extent.Through the T test method we can find that being exposured in marine atmospheric environmental for two years has significant effects on tensile strength and fatigue properties of7050aluminum alloy. The tensile strength of7475aluminum alloy is unaffected, but it has significant effects on fatigue properties of7475aluminum alloy.The F test shows that painting has a significant influence on tensile strength of7050aluminum alloy and7475aluminum alloy.7050aluminum alloy and7475aluminum alloy samples have been exposed in marine atmospheric which non-painted whose surface pitting are more and relatively uniform distribution. But the point of connect with TC18titanium alloy has more serious corrosion and generation of dark gray corrosion products. Whether be painted or not, or assembled with TC18titanium alloy or not, the samples with painting process have no obvious corrosion. The fatigue life of coating samples is higher than unpainted samples, which shows that painting process can prevent atmospheric corrosion and galvanic corrosion in a certain extent.7050aluminum alloy and7475aluminum alloy tensile samples’cracks originated from the second phase particles or defect inside of samples, and the tensile fracture belongs to the second phase particle porous agglomeration fracture. The fatigue crackle of7050aluminum alloy and7475aluminum alloy originates from the surface corrosion area of the samples. Near source area presents the river pattern. We can explain that the marine atmospheric corrosion only produced corrosion on the surface of aluminum alloy. Extension of7050aluminum alloy and7475aluminum alloy has obvious and regular fatigue striation. Transient fault zone can be observed tear ridges and dimples.