L. Blaz

Effect of annealing temperature on the structure and mechanical properties of mechanically alloyed AlMg–Nb2O5 and AlMg–ZrSi2 composites

Mechanical alloying and hot extrusion method were used for manufacturing AlMg‐based composites reinforced with addition of niobium oxide (Nb2O5) and zirconium silicide (ZrSi2) particles. High mechanical properties of the materials were found to result from heavily refined structure of composites. It was found that the composite structure was transformed at high temperature as a result of irreversible chemical reaction between disperse reinforcements and surrounding matrix. Chemical reaction for AlMg–Nb2O5 composite results in a growth of intermetallic grains of Al3Nb type and very fine oxides particles of 5–20 nm in diameter. In the annealed AlMg–ZrSi2 composite, new grains of Al3Zr, Mg2Si and Al(Mg)O are formed as a result of zirconium silicide decomposition. Hot compression tests were performed at constant true strain rate of 5.10−3 s−1 within the temperature range of 293–823 K. The high flow stress values are attributed to highly refined structure of the materials that essentially did not coarsen in spite of high deformation temperature.

Microstructure and Mechanical Properties of Rapidly Solidified Al-Fe-Ni-Mg Alloys

Rapid solidification (RS) combined with following mechanical consolidation of RS powders is considered as a valuable commercial method for the production of a wide range of metallic materials having fine-grained structures. Reported research results for various alloys demonstrate better compositional homogeneity, smaller grain size and relatively fine precipitates distributed homogenously in RS alloys than that for the materials produced by conventional metallurgical processing. The effect of rapid solidification on the microstructure and mechanical properties of selected Al-Fe-Ni-Mg alloys have been investigated. The basic item of the research work was obtaining aluminum PM materials strengthened by highly-dispersed transition metal compounds and aluminum-magnesium solid solution. Rapid solidification (RS) of Al-4Fe-4Ni and Al-4Fe-4Ni-5Mg alloys was performed by means of gas atomizing of the molten alloy and the spray deposition on the rotating water-cooled copper roll. Using typical powder metallurgy (PM) methods, i.e. cold pressing, vacuum degassing and hot extrusion, the RS-flakes were consolidated to the bulk PMmaterials. For comparison purposes, the conventionally cast and hot extruded Al-4Fe-4Ni and Al-4Fe-4Ni-5Mg alloys were studied as well. Mechanical properties of as-extruded materials were examined by compression tests performed at 293 K – 873 K. It was found that relatively high strength of as-extruded PM materials was accompanied by high ductility of samples deformed by hot compression test. Structural observations confirmed beneficial influence of rapid solidification on effective refining of intermetallic compounds, although some inhomogeneity of fine precipitates distribution was observed. Nevertheless, it was considered that an effective increase of the microhardness and strength of tested RS materials mostly result from achieved dispersion of structural components and can be intensified by solid solution hardening due to Mg-addition.

The influence of current density and bath composition on the electrodeposition of nickel and nickel/silicon carbide composite

SUMMARY Electrodeposited nickel and nickel/silicon carbide composite coatings were obtained in a Watts-type bath. The influence of organic additives and current density on the microstructure and the grains size of the deposits was studied and the relationship between the nickel microstructure and the internal stress of deposits evaluated.

Structural and Mechanical Features of Rapidly Solidified Al-2Fe-2Ni-5Mg Alloy

Rapid solidification (RS) of Al-2Fe-2Ni-5Mg alloy and following mechanical consolidation of powders by means of powder metallurgy (PM) methods was used with success to produce a bulk RS-material. RS powders were manufactured using an inert gas atomizing of the molten alloy and the spray deposition on the rotating water-cooled copper roll. Rods of 7 mm in diameter were received by means of the cold pressing of the flakes, vacuum degassing and hot extrusion method. For comparison purposes, the conventionally casted and hot extruded Al-2Fe-2Ni-5Mg alloy was tested as well. Mechanical properties of as-extruded materials were examined at 293 K – 873 K by compression tests performed at constant true strain rate of 5·10-3[s-1]. It was found that relatively high strength of as-extruded RS/PM material was accompanied by the high ductility of the samples deformed by hot compression tests. It was noticed that the most effective solution strengthening due to particles refining was observed at low deformation temperatures. Rising the test temperatures above ~ 420 K, was found to result in reduction of the flow stress to the values received for the industrial material (IM).The formation of coarse primary intermetallic compounds, which is typical for IM material, was effectively reduced for RS material. However some inhomogeneity of fine precipitates distribution in RS/PM material was observed. Nevertheless, it was considered that both solid solution hardening due to Mg addition and the dispersion strengthening due to refining of intermetallic compounds substantially increase the mechanical properties of the RS/PM material.

Microstructure and mechanical properties of AA7039+20%SiC W composite.

Hot deformation tests were performed on an AA7039‐matrix composite reinforced with a 20% addition of SiC whiskers. The flow stress maximum was reduced with deformation temperature from 640 MPa to ∼8 MPa at 293 K and 823 K, respectively. TEM observations, performed on as deformed samples, revealed a highly recovered substructure of the matrix and a striated structure of the whiskers. The fringes, which are perpendicular to the whiskers’ longitudinal axis, were ascribed to nano‐sized twins and stacking faults formed during the crystal growth rather than to some effects of the deformation process.

Structure and Properties Studies of Rapidly Solidified Al-Mn Alloys

Rapid solidification (RS) combined with plastic consolidation by hot extrusion was used to produce Al alloys with additions of varied concentration of Mn. RS flakes were manufactured using an inert gas atomizing of the molten alloy and the spray deposition on the water-cooled cooper roll. Rods of 7mm in diameter were received using cold pressing of RS-flakes, vacuum degassing and hot extrusion procedures. Mechanical properties of as extruded materials were tested in hot compression at temperature range 293K - 773K. It was found that the flow stress was reduced monotonically with deformation temperature for all tested materials. RS alloys exhibit higher mechanical properties than those produced by conventional metallurgy methods. Higher mechanical properties of RS materials are ascribed to beneficial particles morphology obtained due to the rapid solidification. Development of fine Al6Mn particles was observed in all tested RS-materials.

Structure Evolution in Annealed and Hot Deformed AlMg-CeO2 Composite

A brief review of structural investigation and results of mechanical tests for mechanically alloyed AlMg-based composite reinforced with 9 wt.% addition of CeO2 is presented. The as extruded and annealed samples were examined by means of SEM, TEM and X-ray analysis. Heavily refined matrix grains and particles of cerium oxides were observed in the as extruded material. Fine microstructure attained by mechanical alloying and high affinity of oxygen to aluminum-magnesium matrix results in promoted solid state reactions between the matrix and reinforcements at elevated temperatures. Consequently, Al4Ce intermetallic grains and Al/Mg oxides are formed in the result of CeO2 decomposition. Hot compression tests were performed at constant true strain rate of 5·10-3 s-1 within the temperature range of 293 – 823K. Highly refined structure of the material was found to result in high strength of the composite, particularly for samples tested at low and intermediate temperatures.

Mechanical and Structural Characterization of Rapidly Solidified Al-Fe-Mg Alloys

Series of experiments on a series of Al-Fe-Mg alloys were performed to determine the effect of rapid solidification (RS) on the material strengthening, which result from the refining of thegrain size and intermetallic compound. Additionally, an enhancement of the material strengthening due to magnesium addition was also observed. Manufacture of RS Al-Fe-Mg alloys combined a spraydeposition of the molten alloy on the rotating water-cooled copper roll and plastic consolidation bymeans of powders pressing and hot extrusion methods. The results suggest that the rapid solidification provides an effective method of microstructure refinement and, in combination with solid solutionhardening due to Mg, leads to significant improvement of mechanical properties of Al-Fe-Mg based alloys.

An Analysis of the Microstructure and Mechanical Properties of Rapidly Solidified Al-1Fe-1Ni-5Mg Alloy

Experiments on Al-1Fe-1Ni-5Mg alloy were performed to determine the effect of rapid solidification (RS) on the material strengthening, which result from the refining of the grain size and intermetallic compounds. Additionally, an enhancement of the material strengthening due to magnesium addition was also observed. RS procedure was performed using spray deposition of the molten alloy on the rotating water-cooled copper roll. As a result, highly refined structure of rapidly solidified flakes was obtained. Using common powder metallurgy (PM) techniques, i.e. cold pressing, vacuum degassing and hot extrusion, as received RS-flakes were consolidated to the bulk PM materials. For comparison purposes, the conventionally cast and hot extruded Al-1Fe-1Ni-5Mg alloy was studied as well. RS process combined with hot pressing and extrusion procedure was found to be very effective method for the manufacture of fine grained material and effective refinement of intermetallic compounds. However some inhomogenity of particles distribution was observed, which was ascribed to varied cooling rate dependent on the particular spray-drop size. Mechanical properties of as-extruded material were examined using compression test at 293K – 873K. High strength and ductility of as-extruded RS material with respect to conventionally produced alloy were observed. However, the effect of enhanced mechanical properties of RS material is observed only at low deformation temperatures. It was found that increasing deformation temperature above 400K results in negligible hardening of RS samples if compared to conventionally produced material.

Structural Characterization of Mechanically Alloyed AlMg-CeO2 Composite

A mechanical alloying and hot extrusion method was used to manufacture an AlMg-based composite reinforced by ~9 wt.% addition of CeO2. Structural features of as-extruded and re-melted samples were characterized by SEM/TEM observations and XRD analysis. Highly refined structure with uniform distribution of structural components has been received. It was found that during mechanical alloying and following hot pressing and extrusion of the material the decomposition of CeO2 oxides has been initiated. As result, formation of intermetallic grains of Al4Ce type was observed. Thermal analysis experiments combined with structural characterization allowed to determine the equilibrium state of the AlMg-CeO2 composite structure.