Einfluss von Vorkorrosion auf die statische und zyklische Festigkeit von Al-Druckgussbauteilen

Research output: ThesisMaster's Thesis

Organisational units

Abstract

The durability of high pressure die cast aluminium automotive components decreases due to the corrosive environment. There is no general model to evaluate the damaging effect of the corrosive service loading, therefore component tests have to been made. Within this thesis such tests are performed to quantify the decrease of the durability. For that purpose, four different series of components have been corroded prior to the mechanical testing. The testing results of those series are compared to the results of the non-corroded components. The time of the corrosive loading, starting with the non-corroded components, increases by equal time steps from one series to the next, facilitating four different corrosion stages. The prior-testing corrosive damage is analysed with polished metallographic samples of the first two corrosion stages. Whereby the position of those samples matches the highly-stressed zones of the components. Both pitting and intergranular corrosion are identified. The maximum penetration depth of the corrosion is measured at the top of the intergranular corrosion and is around 250μm, this corresponds to a damage of about 5% of the wall thickness. The quite strong corrosive attack is caused by the relatively high copper content of the alloy. With a specially developed test device for the components it is possible to load them as in service. The whole test device with the built-in component is simulated numerically to determine the stresses in the component. The simulation results are verified by several strain measurements with strain gauges during testing. The evaluation of the quasistatic tensile tests shows a significant decrease of the ultimate load for all four corrosion stages due to the corrosive damage. Overall, a linear decrease of 5% of the breaking load for every corrosion stage occurs. In the fatigue tests, the first two corrosion stages are tested in addition to the non-corroded components. The durability of the components of the first corrosion stage decreases up to 40 %, depending on the load level. The second corrosion stage shows with a 60 % decrease in durability, compared to non-corroded components, even a greater corrosive damaging effect. This reduction of both the tensile strength and the durability is caused by the stress concentration due to the pitting and intergranular corrosion. These findings contribute to the understanding on the fatigue properties of automotive components caused by the damaging effects of precorrosion. This makes it possible to consider the effects of corrosion already in the design phase.

Details

Translated title of the contributionInfluence of precorrosion on the static and cyclic strength of Al high pressure die cast components
Original languageGerman
QualificationDipl.-Ing.
Awarding Institution
Supervisors/Advisors
Award date28 Jun 2019
Publication statusPublished - 2019