Abstract
The present work is associated with research concentrating on the innovation and use of hybrid heat treatment for eutectoid steel powder (0.8 wt%) reinforced Al-Zn-Mg (Al 7075) alloy composites. Due to high hardness, wear resistance, tensile strength and flexibility modifying heat treatment, heat treatable aluminium metal matrix composites reinforced with heat treatable hard steel particles may be the choice to explore. In this work, an attempt is made to increase hardness and tensile properties to higher levels through hybrid heat treatment, comprising simultaneous treatment to matrix and reinforcement in 3 different routes (Pearlite, Bainite and Martensite) compared to conventional age hardening treatment. SEM images and microhardness distribution witnessed the phase transformation in both matrix and reinforcement. Aging kinetics in conventional age hardening and hybrid treatments is accelerated by the increase in the quantity of reinforcement and increase in aging temperature. The improvement in hardness and tensile strength obtained by conventional age hardening path is further improved by the hybridisation path. Hybridisation route with martensite reinforcement phase shows excellent result in hardness, strength followed by bainite and pearlite path respectively in the decreasing order. In all heat treatment cycles, lower aging temperature marks greater property enhancement compared to higher temperature. Al 7075 with 6 wt% steel powder reinforced (martensite form) composite showed excellent peak age hardness, tensile strength compared to lesser quantity reinforced composites.
Highlights
Heat treatment is the controlled heating and cooling process of metal alloys and composites for property modification by precise phase transformation in the solid state with optional change in concentration of alloying elements and shape
In composites, only matrix material is subjected to heat treatment and not the reinforcements
Age hardenable alloys like aluminium (2XXX, 7XXX, 6XXX series), Copper (Cu-Be), Titanium (Ti-Al) systems with or without the addition of reinforcement are prone to age hardening with property alterations, like hardness and strength[5,6,7,8,9,10,11,12]
Summary
Heat treatment is the controlled heating and cooling process of metal alloys and composites for property modification by precise phase transformation in the solid state with optional change in concentration of alloying elements and shape. Strength and impact resistance of the material is possible compared to existing methods if the process variables are tailored suitably. Steels and nonferrous metals are generally subjected to conventional (annealing, normalizing, hardening, tempering etc.) and precipitation supported heat treatments (age hardening and thermomechanical processes). In composites (metal matrix composites), only matrix material is subjected to heat treatment and not the reinforcements. Age hardenable alloys like aluminium (2XXX, 7XXX, 6XXX series), Copper (Cu-Be), Titanium (Ti-Al) systems with or without the addition of reinforcement are prone to age hardening with property alterations, like hardness and strength[5,6,7,8,9,10,11,12]
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