This study examined the damage evolution and fracture behaviour oftwo
aluminum automotive alloys as a function ofvarious material and testing variables. When
applicable, the observations were plotted in stress-strain space in order to construct
fracture mechanism maps as functions ofpressure and temperature.
The influence ofiron content was examined through the use oftwo different iron
contents for each ofthe two alloy systems. For the solution hardened 5754 alloy, it was
found that the presence ofincreasing iron content led to more rapid void nucleation,
growth and coalescence which produced a decrease in ductility, and change in fracture
mode from cup and cone to shear MVC. No change in fracture mode was observed with
increasing iron content for the age hardenable 6111 alloy in the T4 temper. However, a
decrease in ductility was observed. The Iow-Fe 6111 T6 alloy was found to fail
intergranularly, while the high-Fe variant was observed to fail by shear MVC. It was
proposed that this was the result ofthe grain refining effects ofthe increased iron content.
The evolution of damage was examined by performing uniaxial tensile test under
superimposed hydrostatic pressure. In this way, the amount ofdamage generated within
the sample during straining could be controlled and its effect on the fracture process
examined. The application ofpressure was found to decrease the amount ofdamage
present in all samples tested and universally increased the observed ductility. When
tested under sufficient pressure, it was found that the 5754 and 6111 T4 alloys would
change fracture modes and fail by ductile rupture, with the damage processes suppressedor completely eliminated. Pressure was found to suppress the intergranular fracture mode
in the Iow-Fe 6111 alloy, causing a transition to the shear MVC mode offailure.
The effect oftemperature on the flow behaviour ofthe 5754 was also examined,
as this alloy was found to exhibit the temperature sensitive Portevin Le Chatelier effect.
The serrated yielding associated with the effect was found to be greatly reduced testing at
77 K, and grain scale and large scale shear processes within the material were observed to
be almost completely eliminated. This was found to lead to large increases in uniform
elongation, and a change in fracture mode from cup and cone to shear MVC for the IowFe variant.ThesisMaster of Engineering (ME
