High Strength Al Alloy Thin Films: A Nanoscale Analysis of Microstructure and Interface Segregation*

Aluminum alloy (AA) 7075 is commonly used in industries for manufacturing highly stressed structural materials including various parts of commercial aircraft, aerospace and transportation equipment because of its extremely high strength to density ratio. This yield strength relies primarily on the microstructural properties, particularly the structure (types, frequency, and connectivity), geometry (inclination and dihedral angle), and chemistry (segregation and precipitation) of the grain boundaries. Herein, experimental results on the microstructural features and atomic scale Cu grain boundary segregation of high strength Al alloy 7075 thin films are analyzed in detail using advanced microscopic characterization techniques. Two distinct types (point and parallel array) of Cu grain boundary segregation behavior are demonstrated for the Al alloy GBs for the first time; GBs misorientated by less than 28^o displayed point (highly segregated atomic column surrounded by low segregated columns) segregation behavior whereas more than the 28^o displayed parallel array (two highly segregated columns opposite to each other across the interface surrounded by low segregated columns) segregation behavior.