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    Effect of alternative heat-treatment parameters on the aging behavior of short-fiber-reinforced 2124 al composites
    (Inst Za Kovinske Materiale I In Tehnologie, 2016) Altunpak, Yahya; Aslan, Serdar; Güler, Mehmet Oğuz; Akbulut, Hatem
    The 2124 Al alloy and a composite of the 2124 Al alloy reinforced with 20 % of volume fractions of delta-Al2O3 short fibers made by squeeze casting were subjected to controlled and systematic aging treatments. The materials were solution treated at (495, 525 and 555) degrees C. After quenching, the matrix alloy and the composite were artificially aged at (160, 170, 180 and 190) degrees C up to 36 h. The aging was monitored with hardness measurements and differential scanning calorimetry. The time required to reach the peak hardness of the composite matrix during a precipitation treatment was shorter than that for the unreinforced 2124 Al. An increase in the solution-treatment temperature resulted in an increase of the composite-matrix hardness. The delta-Al2O3-reinforced composite exhibits no grain-boundary melting, but appears to show incipient melting around short alumina fiber interfaces at temperatures above 525 degrees C. The highest HV value was obtained after solutionizing at 495 degrees C for 6 h, followed by water quenching and aging at 190 degrees C for 10 h for the unreinforced matrix alloy. In the case of the reinforced alloy the highest HV value was found after solutionizing at 555 degrees C for 6 h, quenching and aging at 170 degrees C for 12 h.
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    The effect of plasma spraying on the microstructure and aging kinetics of the Al-Si matrix alloy and Al-Si/SiC composites
    (Springer, 2010) Altunpak, Yahya; Akbulut, Hatem; Üstel, Fatih
    The Al-Si (LM 13)-based matrix alloy reinforced with SiC particles containing 10, 20, and 30 vol.% SiC particles were spray-formed onto Al-Si substrates. The sprayed samples were directly subjected to a standard aging treatment (T551). From the experiments, it was observed that the high rate of solidification resulted in very fine silicon particles which were observed as continuous islands in the matrix and each island exhibited several very fine silicon crystals. Analysis showed that plasma-spraying caused an increased solid solubility of the silicon in the aluminum matrix. DSC measurements in the permanent mold-cast Al-Si matrix alloy and plasma-sprayed Al-Si matrix alloy showed that plasma-spraying causes an increase in the amount of GP-zone formation owing to the very high rate solidification after plasma-spraying. In the plasma-sprayed Al-Si/SiC composites GP zones were suppressed, since particle-matrix interfaces act as a sink for vacancies during quenching from high plasma process temperature. Introduction of SiC particles to the Al-Si age-hardenable alloy resulted in a decrease in the time required to reach plateau matrix hardness owing to acceleration of aging kinetics by ceramic SiC particles.
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    Effects of aging heat treatment on machinability of alumina short fiber reinforced LM 13 aluminum alloy
    (Springer London Ltd, 2009) Altunpak, Yahya; Akbulut, Hatem
    In this paper, the surface integrity (Ra and Rmax) has been investigated with various aging heat treatment and machinability parameters in an aluminum-silicon based (LM-13) MMCs, produced by infiltration method. The composites have been subjected to heat treatment at different temperatures and times which was discussed in detail in an earlier publication (Altunpak and Akbulut, Teknoloji 8(4):331-339, 2005). In the milling of alumina short fiber reinforced LM-13 aluminum alloys, the surface integrity decreased when feed rate increased. It was found that increasing amount of fiber reinforcement and solutionizing temperature has a significant effect on the surface integrity and sub-surface damage of the materials. Increasing the solutionizing temperature and fiber reinforcement produced higher Ra and Rmax values. Microhardness measurement indicated that the sub-surface damage and the hardness increased by increasing the feed rate and fiber content.
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    Mechanical properties of a squeeze-cast 2124 Al composite reinforced with alumina short fibre
    (Edp Sciences S A, 2017) Altunpak, Yahya; Akbulut, Hatem
    The tensile, flexural and fracture behaviours of alumina short fibre reinforced 2124 Al alloy produced by squeeze-cast method have been investigated. The composite and unreinforced alloys have been subjected to heat treatment at different temperatures and times. The highest yield strength, ultimate tensile strength and flexural strength values were obtained after solution treatment at 495 degrees C for the unreinforced alloy. The optimum mechanical properties of the composite material were obtained at 525 degrees C owing to better fibre-matrix interfacial bonding. The peak aging heat treatment conditions at which maximum hardness values are obtained do not provide maximum strength values in the composite. Increasing solution treatment temperature caused fibre decohesion from the matrix due to porosity formed at the fibre matrix interface.