Kleber S. Cruz

Primary dendrite arm spacing during transient directional solidification of Al alloys with low redistribution coefficients

Particular analytical expressions based on a curve fitting on numerical results for primary dendritic growth have been proposed in the literature to encompass binary alloy systems whose redistribution coefficient (k 0) approaches zero. To date, these expressions have not been checked against experimental results of transient solidification. The present study developed a comparative analysis between the theoretical predictions furnished by such expressions and results from transient solidification experiments with low k 0 aluminum alloys. The analysis has shown that the proposed approach generally describes the primary dendritic spacing during solidification of Al–Sn alloys which are characterized by very low k 0 values as well as by very large solidification ranges.

Numerical and experimental analysis of rapidly solidified laser remelted Al 5wt pct Ni surfaces

The aim of this work was to develop a heat transfer mathematical model based on the finite difference method in order to simulate temperature fields in the laser surface remelting process. Convective heat transfer in the remelted pool was taken into account by using the effective thermal conductivity approach. Theoretical predictions furnished by previous models from the literature were used for validation of numerical simulations performed with the proposed model. Experiments of laser surface remelting of Al-5 wt pct Ni samples were carried out in the present investigation, and numerical simulations were applied for the laser machine operating parameters. The work also encompasses an analysis of microstructural and microhardness variations throughout the resulting treated and untreated zones.

Comparative Analysis of Wear Behavior of Al 7075 Alloy, AISI 1020 and AISI 1045 Carbon Steels

The main objective of this study is to analyze a comparative research about the tribological behavior of Al7075, AISI 1020 and AISI 1045 steels during the ball crater abrasion wear test (Hutchings, 1996) without the presence of lubricants (abrasive slurry). The tests were performed for each alloy with a load equal to 1.4N, during 5, 10, 15 and 20 minutes and the rotation used was equal to 230 rpm. Scanning electron microcopy and optical microscopy were used to characterize the worn samples. The wear resistance was measured by calculating the worn volume (V), with the basis on the diameter of the crater produced by the rotating sphere. [1,2,4]. According to the results, the alloy Al7075 presented the lower wear resistance and the AISI 1020 and AISI 1045 steels obtained a similar wear behavior, probably due to the presence of carbon, which makes the hardness increase. However, when the sliding distance is about 276 m, the wear resistance of AISI 1045 steel falls indicating that AISI 1045 may present lower wear resistance for longer sliding distances

Numerical and Experimental Analysis of Laser Surface Remelting of Al 9wt% Si Alloy Samples

Laser materials processing has been widely applied in industrial processes due to unique precision and very localized thermal action furnished by the laser’s high energy density and power controllability. With the inherent rapid heating and cooling rates to which this surface layer is subjected, this process provides an opportunity to produce different microstructures from that of the bulk metal leading to useful properties. The aim of this work is to develop a heat transfer mathematical model based on the finite difference method in order to simulate temperature fields in the laser surface remelting process. Convective heat transfer in the remelted pool is taken into account by using the effective thermal conductivity approach. Theoretical predictions furnished by previous models from the literature were used for validation of numerical simulations performed with the proposed model. Experiments of laser surface remelting of Al-9 wt pct Si samples was carried out in the present investigation, and numerical simulations was applied for the laser machine operating parameters. The work also encompasses the analysis of microstructural and microhardness variations throughout the resulting treated and unmolten zones.