Salar Bozorgi

Experimental investigations on energy absorption capacity of selected Al–Si–Mg casting alloys

Abstract Three hypoeutectic Fe containing Al–Si–Mg alloys for casting crash relevant automotive components are experimentally investigated. The comparatively short heat treatments include solutionising at 540°C for 5 min or at 465°C for 60 min respectively, compressed air quenching and artificial aging at 223°C for 120 min. Characteristic mechanical parameters are determined by tensile, plate bending and Charpy pendulum impact tests. Intermetallic phases are identified by scanning electron and by light microscopy. The results show that increasing the Mg content promotes the precipitation of Mg2Si particles, which enhance the strength. Increasing the Fe content promotes the formation of intermetallic Fe bearing particles which reduce the energy absorption capacity and the ductility. Increasing the Si content has the similar effect, since the volume fraction of the eutectic phase and the size of the intermetallic particles increase.

A Numerical and Experimental Study of Flow Behavior in High Pressure Die Casting

High pressure die casting (HPDC) is one of the most important and yet little known manufacturing methods especially during liquid metal injection and filling phase. During its application different problems can arise: on the one hand, wavy disintegration of the jet might result in cold shut defect in the final product, on the other hand a high degree of atomization may strongly increase the porosity defect. A numerical simulation using volume of fluid approach (VOF), is carried out to model the global spreading of liquid metal jet. The formation of droplets, which are usually smaller than the grid spacing in computational domain, is determined by a surface energy-based criterion. An Eulerian-Lagrangian framework is introduced to track and model the droplets after formation. Since liquid metal is hardly to access, we performed experiments based on water analogy to capture the flow regime changes and drop formation. The comparison between numerical results and experiments shows a very good agreement.

Untersuchung von Hochtemperatureigenschaften modifizierter AlSiCu-Gusslegierungen

ZusammenfassungIm Rahmen dieser Forschungsarbeit wurde eine modifizierte AlSiCu-Gusslegierung mit einer normierten AlSi9Cu3-Gusslegierung verglichen. Die Werkstoffe werden vorwiegend in der Automobilindustrie für die Kolben- und Zylinderkopfproduktion verwendet. Dies resultiert aus der guten Gießbarkeit, der hohen Festigkeit bei Raumtemperatur und erhöhter Temperatur, dem geringen Gewicht, der guten Verschleißfestigkeit und der geringen Wärmeausdehnung [1].Die Art der Modifizierung erfolgte durch eine Zugabe der Legierungselemente Cr und Mo, zusätzlich wurde der Cu-Gehalt auf ca. 6 % erhöht. Um unterschiedliche Wandstärken zu untersuchen, wurden mit dem Squeeze-Casting-Verfahren auf der UBE350 Stufenplatten abgegossen, davon drei Werkstoffzustände und zwei unterschiedliche Wandstärken betrachtet. Dabei wurden zwei Wärmebehandlungsvarianten mit dem Gusszustand verglichen und zur Charakterisierung der mechanischen Eigenschaften Zugversuche bei Raumtemperatur und erhöhter Temperatur (240 °C) durchgeführt. Um die mechanischen Eigenschaften in Kombination mit der Mikrostruktur zu untersuchen, wurden mit der Hilfe von LIMI und REM inklusive EDX-Analyse metallografische Untersuchungen angestellt.Die Modifikationen zeigte eine wesentliche Verbesserung der Dehngrenze und Zugfestigkeit sowohl bei Raumtemperatur als auch bei einer Prüftemperatur von 240 °C.AbstractWithin this research one modified AlSiCu master casting alloy has been compared with the norm AlSi9Cu3 casting alloy. These alloys are mainly used in the automotive industry for pistons and cylinder heads. The good castability, the high strength at room and elevated temperatures, the low weight, the good wear resistance, and the low thermal expansion are responsible for these applications.The modification was based on an addition of Cr and Mo. In this alloy the Cu content was increased to 6 %. Thus, step plates were cast with the squeeze casting process at the UBE350 machine to compare two different wall thicknesses. The alloys were investigated in the as cast condition as well as in two different heat treatment conditions. To characterize the mechanical properties, tensile tests at room temperature and hot tensile tests at 240 °C were performed. To explain the results in connection with the microstructure, metallographic examinations with LIMI and SEM including EDX were made.The results show that the modification improves the yield strength at room and elevated temperatures in comparison to the norm alloy.

Microstructures and mechanical properties of Er modified AA7075 alloy

ABSTRACT The effect of erbium and homogenization on microstructures and mechanical properties of AA7075 alloy were investigated using optical microscope (LIMI), scanning electronic microscope (SEM) equipped with energy dispersive X-ray detection (EDS) and mechanical testing. It was found that during solidification most of the elements Er and Cu segregated at the grain boundaries in the form of Al3ErCu or Al8Cu4Er and a very small part of Er dissolved in the FCC-Al matrix. The latter is not completely reclaimable for heterogeneous nucleation and refine grain FCC-Al matrix in its as-cast state. Er and Cu- containing phases fragmented into fine particles after extrusion and these led to a slight increase in grain boundary strengthening. The process of homogenizing, extruding and aging the Er containing alloys considerably improved the strength due to precipitation. The analysis of the extruded sample showed that the addition of Er can slightly retard the recrystallizing behavior of AA7075 alloy.

Prediction of Surface Porosity Defects in High Pressure Die Casting

High pressure die casting (HPDC) is a novel manufacturing method with capability of mass production with higher accuracy. Porosity is one of the challenging defects in final product and may be affected by jet instability and atomization during injection phase. In case of atomization a large number of droplets with high velocity impinges the colder confining walls of the casting mold and might solidify consecutively. Different time scales of the impingement of the droplets and their solidification may result in heterogeneous structures near the surface of final product. A numerical framework using volume of fluid method (VOF) and an Eulerian-Lagrangian approach is established to simulate the liquid metal jet breakup and droplet formation during the injection phase. An analytical model for droplet impact on mold walls and solidification is studied and implemented in the numerical framework. The latter enables the prediction of porosity formation near the surface of final product.

Effect of Heat Treatment and Alloying Element on Impact Energy Absorption of AlSi10 Casting Alloys

The automotive applications using heat-treatable aluminum cast alloys are designed for high impact energy which can be improved using specified casting process and different heat treatment. In this study an economical and convent squeeze casting machine was used to produce the u-profile with 3mm wall thickness under controlled solidification conditions. The casted samples were used for mechanical and metallographical characterization. The mechanical properties of alloys containing different amount of Fe, Mn und Mg were determined as a function of different heat treatment condition such as modified T7 and Silicon Spheroidization Treatment (SST). The microstructure of casted alloys were quantificational determined by a combination of light optical microscope and scanning electron microscope (SEM) equipped with an energy dispersive spectroscopy (EDS) module to identify the morphology and chemical composition of intermetallic eutectic phases. The results of Charpy impact test show that impact energy increases after modified T7 or SST heat treatment significantly compared with the as cast state. Furthermore the impact energy is less in the higher Mg containing alloys (0.15wt.%) compared with the less Mg containing alloy (0.07wt.%).