Haider T. Naeem

Effect of friction stir processing on the microstructure and hardness of an aluminum-zinc-magnesium-copper alloy with nickel additives

The main object of this study is to investigate the effect of friction stir processing (FSP) on the microstructure and hardness of Al-Zn-Mg-Cu alloys that were produced via casting with the addition of 5 wt % nickel. Furthermore, a single-pass FSP with a rotational speed of 1500 rpm and a traveling speed of 40 mm/min was performed on the alloys. The FSP-treated cast alloys were homogenized, aged at 120°C for 24 h, retrogressed at 180°C for 30 min, and then re-aged at 120°C for 24 h. Microstructural evaluations via optical microscopy and scanning electron microscopy, as well as with energy dispersive X-ray spectroscopy were conducted. In addition, X-ray diffraction analysis was performed to detect the intermetallics and phases of the Al-Zn-Mg-Cu-Ni alloys. Before FSP, the microstructural observations indicated the presence of coarse Ni dispersed particles with a precipitate phase within the matrix. After FSP treatment, the grain refinement led to the uniform space distribution of Ni dispersed particles in the stir zone. The Vickers hardness values for the Al-Zn-Mg-Cu-Ni alloy increased after age tempering at T6 and retrogression and re-aging (RRA) treatment because of the increased precipitation and particles dispersity. The hardness of the Al-Zn-Mg-Cu-Ni alloy was enhanced after FSP and a series of heat treatments, especially the RRA process, because of the stirring action of the FSP tool, the grain refinement, the appearance of additional precipitates, and the refinement of dispersed Ni particles.

The Influence of Nickel and Tin Additives on the Microstructural and Mechanical Properties of Al-Zn-Mg-Cu Alloys

The effects of nickel and nickel combined tin additions on mechanical properties and microstructural evolutions of aluminum-zinc-magnesium-copper alloys were investigated. Aluminum alloys containing Ni and Sn additives were homogenized at different temperatures conditions and then aged at 120°C for 24 h (T6) and retrogressed at 180°C for 30 min and then reaged at 120°C for 24 h (RRA). Comparison of the ultimate tensile strength (UTS) of as-quenched Al-Zn-Mg-Cu-Ni and Al-Zn-Mg-Cu-Ni-Sn alloys with that of similar alloys which underwent aging treatment at T6 temper showed that gains in tensile strengths by 385 MPa and 370 MPa were attained, respectively. These improvements are attributed to the precipitation hardening effects of the alloying element within the base alloy and the formation of nickel/tin-rich dispersoid compounds. These intermetallic compounds retard the grain growth, lead to grain refinement, and result in further strengthening effects. The outcomes of the retrogression and reaging processes which were carried on aluminum alloys indicate that the mechanical strength and Vickers hardness have been enhanced much better than under the aging at T6 temper.

The Effect of Microalloying of Nickel, RRA Treatment on Microstructure and Mechanical Properties for High Strength Aluminum Alloy

High strength aluminum alloys Al-Zn-Mg-Cu-(0.1) Ni produced by semi-direct chill casting process were homogenized at different conditions then conducted heat treatment process which comprised pre-aging at 120°C for 24 h, retrogression at 180°C for 30 min, and then re-aging at 120°C for 24 h. Microstructural studies showed that add Ni (0.1 wt %) to the alloy will be forming Ni-rich phases such as AlCuNi, AlNi, AlNiFe and AlMgNi which provide a dispersive strengthening affected in the solid-solution and the subsequent heat treatments. The results showed that by this three-step process of heat treatments, the mechanical properties of aluminum alloys Al-Zn-Mg-Cu-(0.1) Ni were substantially improved. The highest attain for the ultimate tensile strength and Vickers hardness for the alloy sample after applied the retrogression and reaging process is about 545 MPa and 237 HV respectively.

The Role of Direct Chilling, Retrogression and Reaging Treatment on Mechanical Properties of High Strength Aluminum Alloy

The effect of retrogression and reaging heat treatment on microstructure evolution andmechanical properties of 7075 Al alloy in direct chilling casting process was investigated. The subsequent heat treatment process comprised pre-aging at 120°C for 24 h, retrogression at 180°C for 30 min, and then reaging at 120°C for 24 h. By this three-step process, the mechanical properties of the chilled casted samples were substantially improved. The samples retain their high strength at T6 level. They gave yield strength up to 290 MPa, ultimate tensile strength of 386 MPa and elongation of 5.9%. The average value of multiple Vickers hardness tests results were in the range of 210 Hv. The direct chilling process followed by retrogression and reaging heat treatment yielded casts of fine and uniform microstructure as opposed to the microstructure of samples casted by the conventional process.

Effect of milling parameters on the synthesis of Al–Ni intermetallic compound prepared by mechanical alloying

Nanocrystalline Al–Ni intermetallic compounds were synthesized with different percentages of nickel by mechanical alloying (MA) of elemental powders. In all MA runs, the ball-to-powder weight ratio was 10:1, the rotation speed was 350 rpm, and the milling time ranged from 4 to 12 h. The phase evolution and microstructural changes of the powders during MA were investigated by X-ray diffraction (XRD), scanning electron microscopy, and energy-dispersive X-ray spectroscopy analyses. The crystallite sizes of milled powders were estimated based on the broadening of XRD peaks using the Williamson–Hall formula. Results showed that an optimum MA time of 12 h led to the formation of solid solutions of Al–Zn–Mg and Ni, which can be added to many Al–Ni intermetallic compounds. Furthermore, an Al–Ni intermetallic phase with <20 nm crystallite size was obtained.

The Role of cobalt and nickel intermetallic phases on the mechanical properties and microstructure evolution of Al-Zn-Mg-Cu alloys

In this study, the effects of cobalt and nickel additions on microstructure evolution and mechanical properties of Al-Zn-Mg-Cu alloys produced by chill casting process were investigated. Al-Zn-Mg-Cu aluminum alloys containing Ni and Co additives were homogenized at different heat treatment conditions, aged at 120oC for 24 h, and retrogressed at 180oC for 30 min then re-aged at 120oC for 24h. Comparison of the ultimate tensile strength of the Al-Zn-Mg-Cu base alloy underwent RRA temper process with that of the base alloy underwent a similar heat treatment process after the addition of 0.5 wt. % Ni and 0.5 wt. % Co showed that the gains of tensile strengths of the orders of 100 MPa and 135 MPa were attained respectively. These improvements are attributed to phase dispersion particles of the formation of Ni and Co-rich such as Al7Cu4Ni, Al75Ni10Fe15, Al3Ni2 and Al70Co15Ni15. The dispersed particles of nickel or/and cobalt have improved the ultimate tensile strength to reach 630 MPa and 665 MPa and the hardness HV values to 250 MPa and 265 MPa respectively. Besides dispersion, Ni and Co intermetallic dispersoids retarded the grain growth, led to grain refinement and precipitation hardening and resulted in further strengthening of the Al alloy. Microstructure characterization of the alloys was carried out using optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD).

Evolution of the Retrogression and Reaging Treatment on Microstructure and Properties of Aluminum Alloy (Al-Zn-Mg-Cu)

In this study the evolution of the retrogression and reaging (RRA) heat treatment process on microstructure and mechanical properties of AA 7075 Al-alloys which produced by semi-direct chill (DC) casting process were investigated. Al-Zn-Mg-Cu alloys were homogenized at different heat treatment conditions, aged at 120°C for 24 h (T6), and retrogressed at 180°C for 30 min then re-aged at 120°C for 24 h (RRA). The results showed that this three-step process of the heat treatments, the mechanical properties of alloys was substantially improved. The highest ultimate tensile strength and Vickers hardness attained for the retrogression and re-aging about 530 MPa and 223 HV respectively. The precipitation strengthening is responsible about improve the strength under impact the retrogression and re-aging process.

Study of the feasibility of producing Al–Ni intermetallic compounds by mechanical alloying

Mechanical alloying (MA) was employed to synthesize Al–Zn–Mg–Cu alloys of high weight percentage of the nickel component from the elemental powders of constituents via high-energy ball milling. The mixed powders underwent 15 h of milling time at 350 rpm speed and 10: 1 balls/powder weight ratio. The samples were cold-compacted and sintered thereafter. The sintered compacts underwent homogenization treatments at various temperatures conditions and were aged at 120°C for 24 h (T6). The milled powders and heat-treated Al alloy products were characterized via X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). The crystallite sizes and microstrains of the alloyed powder were estimated via measuring the broadening of XRD peaks using the Williamson–Hall equation. The results have revealed that optimum MA time of 15 h has led to the formation of Al-based solid solutions of Zn, Mg, Cu, and Ni. The outcomes showed that the Vickers hardness of the sintered Al–Zn–Mg–Cu compacts of Ni alloys was enhanced following aging at T6 tempering treatments. Higher compression strength of Al-alloys with the addition of 15% nickel was obtained next to the aging treatment.

Assessment of retrogression and re-aging treatment on microstructural and mechanical properties of Al-Zn-Mg-Cu P/M alloy

In order to understand the importance of the retrogression and re-aging as a heat treatment for improving microstructural and mechanical properties of the Al-Zn-Mg-Cu powder metallurgy alloys, Al-Zn-Mg-Cu-Fe-Cr alloys were fabricated from the elemental powders. Green compacts are compressed under compaction pressure about 370 MPa. The sintering process carried out for the samples of aluminum alloys at temperature was 650°C under argon atmosphere for two hours. The sintered compacts were subjected into homogenizing condition at 470°C for 1.5 hours and then aged at 120°C for 24 hours (T6 temper) after that it carried out the retrogressed at 180°C for 30 min., and then re-aged at 120°C for 24 hours (RRA). Observations microstructures were examined using optical, scanning electron microscopy coupled with energy dispersive spectroscopy and X-ray diffraction. Density and porosity content was conducted for the samples of alloys. The result showing that the highest Vickers hardness exhibited for an Al-Zn-Mg-Cu al...

Influence cobalt on microstructural and hardness property of Al-Zn-Mg-Cu-Fe-Cr-Ni P/ M alloys

In this study, influence cobalt additives on the microstructural and hardness properties of an Al-Zn-Mg-Cu-Fe-Cr-Ni PM alloy undergone the retrogression and re-aging treatment were carried out. Green compacts pressed at 370 MPa were then sintered at temperature 650°C in argon atmosphere for two hours. The sintered compacts subjected to a homogenizing treated at 470°C for 1.5 hours then aged at 120°C for 24 hours and retrogressed at 180°C for 30 minutes, and then re-aged at 120°C for 24 hours. Microstructural results of the Al-Zn-Mg-Cu-Fe-Cr-Ni-Co alloys introduced an intermetallics compound in the matrix of alloy, identified as the Al5Co2, Al70Co20Ni10 and Al4Ni3 phases besides to the MgZn2 and Mg2Zn11 phases which produced of the precipitation hardening during heat treatment. These compounds with precipitates provided strengthening of dispersion that led to improved Vickers’s hardness and dinsifications properties of the alloy. The highest Vickers hardness of aluminum alloy containing cobalt was gotten a...