Characterization of quasicrystalline precipitates in artificially aged Al–Mg–Zn alloy with Ga addition

This work present studies on microstructures and mechanical properties of two conventionally cast Al–Mg–Zn base alloys subjected to aging process: Al-2.7Mg-2.1Zn and Al-2.2Mg-1.8Zn-1.1Ga (at.%). Both alloys were homogenized, solution treated and aged isothermally at 473 K (200 °C). Maximum hardness in the base and the Ga-modified alloy was reached after 4 h of aging, however the Ga–bearing sample demonstrated much higher hardness values and tensile strength. The difference correlates with the high precipitate number density estimated for this sample. Based on electron diffraction data, the structure of formed precipitates differs between the ternary and the Ga-modified material. Studies using a transmission electron microscope (TEM) indicated that η and η′ precipitates are present in the peak-aged microstructure of the Al-2.7Mg-2.1Zn alloy, while in the Ga-bearing sample icosahedral quasicrystalline and T-phase precipitates are formed. A crystallographic relationship between the I-phase precipitates and the Al matrix were analyzed in detail along different zone axes of the Al lattice

Formation of a Quasicrystalline Phase in Al–Mn Base Alloys Cast at Intermediate Cooling Rates

Al-rich 94Al–6Mn and 94Al–4Mn–2Fe alloys were suction-cast to evaluate thefeasibility of obtaining bulk quasicrystal-strengthened Al-alloys at intermediatecooling rates alloyed with non-toxic, easily accessible and affordable additions.The influence of different cooling rates on the potential formation of a quasicrystallinephase was examined by means of scanning and transmissionelectron microscopy, X-ray diffraction and differential scanning calorimetry.Increased cooling rates in the thinnest castings entailed a change in samplephase composition. The highest cooling rates turned out to be insufficient toform an icosahedral quasicrystalline phase (I-phase) in the binary alloy. Instead,an orthorhombic approximant phase occurred (L-phase). The addition of Fe tothe 94Al–6Mn binary alloy enhanced the formation of a quasicrystalline phase.At intermediate cooling rates of 102–103 K/s, various metastable phases wereformed, including decagonal and icosahedral quasicrystals and their approximants.Rods (1 mm in diameter) composed of I-phase particles embedded in Almatrix exhibited a hardness of 1.5 GPa, much higher than the 1.1 GPa of 94Al–6Mn

Effect of severe plastic deformation process on microstructure and mechanical properties ofAlSi/SiC composite

AlSi11 matrix composites reinforced with SiC particles have been fabricated by high pressure die casting assisted by ultrasonic mixing. Severe plastic deformation process was performed on the as cast AlSi/2wt.%SiC composite using the modified channel with the twisted output (TCAP) at three temperatures of 350, 400 and 450 °C. The TCAP tool consists of helical part in the horizontal area of the channel allowing for simulation of back pressure and thus resulted in the increase of extrusion force and local plastic deformation. The most important issue of the presented investigations was to refine dendritic cast microstructure of the prepared composite during one pass of TCAP. As a result, a composite with a matrix containing equiaxed α(Al) grains of few microns depending on TCAP temperature and β(Si) particles of about 1 μm in size with twinned structure was produced. The dynamic recrystallization process during TCAP at 450 °C manifested by the grain growth of α(Al) and decrease of dislocation density was observed to affect the sample hardness causing its decrease. The mechanical properties of the composite extruded by TCAP were measured by compression testes and the maximum plastic deformation of about 35% and the compressive strength near 300 MPa were observed. These values were similar for all samples extruded at temperatures between 350 and 450 °C and generally are better comparing with AK11 alloy subjected to different plastic deformation processes.Web of Science1796094