The effect of particle reinforcement on the creep behavior of aluminum alloys.

The effect of particle reinforcement on the creep behavior of various aluminum alloys has been studied in the temperature range of 150$\sp\circ$C to 250$\sp\circ$C. Four systems were investigated: 2219 aluminum, pure (99.8) aluminum, and aluminum - 1.5% magnesium, all reinforced with 3.3$\mu$m TiC particles, and 2080 aluminum reinforced with SiC particles. Emphasis is placed on understanding the effect of particle reinforcement on creep resistance, by isolating direct and indirect composite strengthening effects. Matrix microstructure is characterized before and after creep deformation to identify dominant dislocation mechanisms. In 2219/TiC/15p, precipitate spacing determines creep resistance, with creep rate varying with cubic dependence on spacing. When identical microstructures are compared, 2219/TiC/15p is a factor of 2 more creep resistant than unreinforced 2219 at 150$\sp\circ$C. The addition of TiC to pure aluminum increases creep resistance by a factor of 250 times at both 150$\sp\circ$C and 250$\sp\circ$C. In Al-1.5Mg composites, a factor of 2-3 increase in creep resistance is observed, relative to unreinforced Al-1.5Mg at 150$\sp\circ$C. Slightly greater strengthening is observed at 250$\sp\circ$C. The addition of SiC to 2080 aluminum reduces, rather than increases, creep resistance, even when identical microstructures are compared. In 2080 composites, weakening occurs under all conditions when matrix strengthening is determined by precipitation hardening. When 2080 materials are tested under conditions where the matrix precipitates are severely coarsened or dissolved, composite strengthening is observed. Continuum models accurately predict the strengthening observed when matrix microstructure is stable and identical in the composite and unreinforced materials. These conditions exist in 2219 aluminum at 150$\sp\circ$C, Al-1.5Mg at 150$\sp\circ$C, and 2080 composites tested under conditions where solid solution mechanisms control matrix deformation. The large strengthening observed in pure aluminum composites is a result of internal stresses produced by interactions between the reinforcements and the dislocation substructure. Composite weakening in 2080 composites is a result of strain localization near SiC particles which leads to precipitate breakdown.PhDMaterials Science and EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/104156/1/9500973.pdfDescription of 9500973.pdf : Restricted to UM users only