Stress corrosion cracking behaviour of 7xxx aluminum alloys: A literature review

Effects of Sc and Zr microalloying additions and aging time at 120 °C on the corrosion behaviour of an Al–Zn–Mg alloy

The role of magnesium segregation in the intergranular stress corrosion cracking of aluminium alloys

A search for lead-free solder alloys has produced an alloy in the Ag-Cu-Sn system. This alloy is of great importance to the soldering community, and proper determination of structure, processing, and properties will be significant. In the present study, tin-rich alloys were fabricated to better determine the much-debated morphology of secondary and tertiary phases in the eutectic structure. A deep etching procedure was used to reveal the growth structure of monovariant "eutectic-like" reactions as well as the ternary eutectic reaction. Scanning electron microscopy (SEM) and electron-probe microanalysis (EPMA) verified the three-phase nature of the eutectic. The rodlike eutectic structure in this system is consistent with the more simplified volume fraction and surface energy models that have been presented in the literature.

Determination of the eutectic structure in the Ag-Cu-Sn system

The grain-boundary segregation of Mg atoms in a high-purity Al-8wt% Mg alloy, water quenched from the solution heat-treatment temperature, has been investigated by energy dispersive X-ray microanalysis in a TEM/STEM electron microscope. Many grain boundaries showed a segregation of Mg atoms to a level 2 to 3 times higher than the alloy composition. In the as-quenched state, Mg was uniformly distributed along the grain boundaries, but formed clusters during ageing at room temperature. Hydrogen bubbles were often associated with these Mg-rich regions. Mg-depleted zones were observed adjacent to most boundaries, but in most cases on only one side of the boundary.

Grain-boundary segregation in an Al-8 wt % Mg alloy

This study of Al-Zn-Mg alloys was undertaken to establish the specific combination of mechanical and thermal conditions which is necessary for stress-corrosion susceptibility to occur in these alloys. The work included a study by electron transmission microscopy of the microstructure of this alloy system. A new mechanism is proposed to account for the observations made. It suggests that the high corrosion potential at grain boundaries in stress-corrosion susceptibile Al-Zn-Mg alloys is due to segregation of zinc and magnesium. By taking precautions to reduce this segregation, the stress-corrosion life can be increased.

R. L. Edgar

Papers

A study of stress-corrosion in Al-Zn-Mg alloys