Precipitation phenomena in Al-Zn-Mg alloy matrix composites reinforced with B4C particles

Abstract

To provide insight into precipitation phenomena in age-hardening Al-Zn-Mg(-Cu) matrix composites, an Al 7075 alloy composite reinforced with B4C particles was selected as a model system. The bulk composites were fabricated via plasma activated sintering and followed by a peak aged (T6) heat treatment. Two types of Al matrix zones were identified in the composite: (1) the regions in the vicinity of the matrix/reinforcement interface, defined as “matrix plastic zone” (MPZ) hereafter, and (2) the regions away from the matrix/reinforcement interface, simply defined as matrix hereafter. The precipitation behavior in the MPZ was characterized and compared to that in the matrix. The MPZ contained a high density of dislocations. The number density of GP zones in the MPZ is lower than that in the matrix while the average size of the GP zones in MPZ is coarser. In addition, semi-coherent platelet η′ precipitates were observed but only in the MPZ. The dislocations and the Al/B4C interfaces provide more heterogeneous nucleation sites for the η′ precipitates in the MPZ. The growth and coarsening of the η′ precipitates caused rapid depletion of Mg and Zn solute atoms in the MPZ.

The influence of artificial aging on the microstructure and hardness of an Al–Zn–Mg–Zr alloy processed by equal-channel angular pressing

“…There is a large interest in age-hardenable Al-Zn-Mg alloys (7xxx series) due to their technological and practical importance, as these alloys can be treated to have a preferable combination of ductility and strength, as well as reasonable weldability and corrosion resistance. If a supersaturated Al-Zn-Mg alloy is aged under different conditions, various metastable and stable precipitates may form [1][2][3][4][5][6][7][8]. Therefore, aging can be used for tailoring the mechanical behavior of these alloys.…”

Calorimetric Study with Uncertainty Analysis to Investigate the Precipitation Kinetics in a Nanostructured Al Composite

“…The nanoindenation hardness values in the vicinity of the B 4 C/Al interface (4.32 ± 0.64 GPa) are higher than those in the Al matrix regions that are far away from the interface ( x > 1 μm, 3.95 ± 0.36 GPa). The increase in local hardness as the location approaches the B 4 C/Al interface is attributed to the plastic deformation zone (stress field) and the accelerated precipitation behavior in the vicinity of the interface …”

“…Moreover, it has been found that the precipitation behavior changes with a reduction in grain size, and thus conventional heat treatments are not as effective as they are in the conventional coarse grained alloys . In recent studies on bulk B 4 C/Al 7000 series composites after T6 temper, relatively coarser η' precipitates and rod‐like η phase were observed in the vicinity of the B 4 C/Al interface compared to the GP zones and fine η' precipitates in the Al matrix regions that are far away from the interface . These observations indicated accelerated precipitation kinetics occurred at the interfacial regions due to the presence of the B 4 C particles.…”

Silicon Nitride Whisker-Reinforced Aluminum Matrix Composites: Twinning and Precipitation Behavior

“…An accelerated aging response was reported in a number of composite systems, e.g., B 4 C/Al-Zn-Mg alloy [15], SiC p /2014Al [16], and SiC w /Al-Li alloys [17,18]. A mechanism proposed to explain the accelerated aging in AMCs was related to the enhanced nucleation and/or growth of precipitates in the heavily dislocated matrix regions adjacent to the reinforcement [19,20].…”

“…Generally, the precipitation behavior of AMCs depends on the matrix material, type of reinforcements, processing route and aging temperature [11][12][13][14]. Previous studies indicated that the precipitation sequence in AMCs remained the same as the matrix alloys, but the aging kinetics was observed to be changed [5,15].…”