1. Introduction

Laser surface remelting (LSR) has attracted increasing interest in recent years owing to its special capabilities. High energy density of LSR translates into efficient use of energy for remelting, because LSR modifies surface properties of a material without affecting its bulk properties. LSR results in rapid quenching of the molten material by conduction into the cold subsurface after rapid irradiation. This type of behavior was also observed by Kalita [1], who applied laser surface melting (LSM) technique in a study of high strength aluminum alloys (HSAL).

Pariona et al. [2, 3] used LSR technique in a study of hypoeutectic Al-1.5 wt.% Fe alloy. Characterization of the cast region revealed the formation of a refined, dense and highly homogeneous microstructure, as well as cracking, noticeably with a high formation of protuberance on the weld fillets than alloy untreated. An overlapping line of consecutive weld fillets was also perceptible in the cast region of this alloy, which resulted in an increase of about 61% in hardness compared to the base material. According to Pariona et al. [4], which the Marangoni effect influence thermal gradient in the molten pool a high temperature, meanwhile, also it produces effects in quality and properties of microstructure, morphological characteristic and as well as quality of laser-treated workpiece track. Yet these same authors confirmed, at low laser beam velocities, the morphology is higher and quality of track presents many defects than at high laser beam velocities.

power of the laser beam was set at 600 W and the power density on the sample

Al 99.76% 0.09% 0.06% 0.06% 0.03% Fe 99.97% — 0.01% 0.01% 0.01%

Effect of Microstructure on Microhardness and Electrochemical Behavior in Hypereutectic…

2.3 Equipment for microstructural and morphological characterization

Various microstructural characterization techniques were employed to gain a better understanding of microstructural effects of Al-2.0 wt.% Fe alloy LSR-treated under study. These techniques applied were optical microscopy (OM), fieldemission scanning electron microscopy (FESEM) coupled to energy dispersive spectroscopy (EDS) and Vickers microhardness testing, which are described in

LSR treated samples were analyzed by OM (Olympus BX51) couple to a Q-Color

Laser-treated material and substrate were analyzed by FESEM (MIRA 3 LM) coupled to EDS to examine the microstructural changes caused by laser treatment.

Vickers hardness (HV) tests were performed using a Leica VMHT MOT microhardness tester operating with a load of 0.1 kg at 15 seconds (HV 0.1 15 s). The tester was applied in the cross-sectional area of treated specimen, to different penetration depths until it reached the base material. Penetration depths of the tester from the surface in the treated material region were approximately 50, 100 and 200 μm, however, 300, 500 and 700 μm were in the base material region, as shown schematic in Figure 1. At each of these depths, 15 micro-indentations were made in lines parallel to surface. Average hardness and standard deviation at each of

For preparation of HV tests, a cross-sectional sample was sanded with 600 and

The electrochemical impedance spectroscopy (EIS) test was performed in aerated solution of 0.1 M H2SO4 at a temperature of 25 0.5°C, using Autolab PGSTAT 30 potentiostat system connected to a microcomputer. Working electrodes of

1200 grit sandpaper and polished with colloidal silica to reduce its roughness, thereby preventing roughness that could interfering in results of HV measurements. Besides, microhardness was measured on the laser-treated sample surface, which was cleaned only with water to prevent that it could be modified. Furthermore, the

material's hardness was tested on the weld fillets region and between them.

3 digital camera to capture images. Prior to studying the LSR treated layer, the cross-sections were cut of the samples using a diamond blade and they were sanded and polished. Samples were chemically etched with hydrofluoric acid 0.5% (v/v) at intervals 30 to 45 seconds, after they were polished with metallographic polishing

pads, using only water, to ensure LSR treatment would not be impaired.

. Laser-treated samples were covered

Fe Si Cu Ni

surface was estimated at 4.8 <sup>10</sup><sup>5</sup> W cm<sup>2</sup>

DOI: http://dx.doi.org/10.5772/intechopen.81095

2.4 Vickers microhardness testing

selected depths were calculated based on data obtained.

2.5 Electrochemical impedance spectroscopy (EIS) test

detail below.

177

Table 1.

with several weld fillets during the remelting process [8].

Chemical composition of materials used for manufacture of Al-2.0 wt.% Fe alloy.

Material Impurity

Moreover, Trdan and Grum [5] analyzed that laser shock peening (LSP) process enables the improvement of corrosion resistance by means of increased pitting potential with lower intensity of pitting attack on the specimen's surface. Hatamleh et al. [6] confirmed higher corrosion resistance of laser-peened friction stir-welded 7075 aluminum joints in a 3.5% NaCl solution. Although, Pariona and Micene [7] and Pariona et al. [2] analyzed, which during LSR-treatment in Al alloy, the melted zone was constituted of metastable phases by LAXRD analysis and it revealed the presence mainly of Al2O3 and AlN phases. These authors emphasized, which these phases contributed in the microstructural modification, favored the characteristics of high hardness and corrosion resistance of LSR-treated workpiece in sulfuric acid.

This study involved LSR treatment of hypereutectic Al-2.0 wt.% Fe alloy. The samples was characterized by various techniques, including optical microscopy (OM), scanning electron microscopy (SEM), Vickers microhardness test. Analysis of Vickers hardness were done in the cross-sectional area of treated sample and on the treated sample surface. Furthermore, the electrochemical impedance spectroscopy (EIS) test was studied and their numerical simulation was done. The microstructure microhardness and electrochemical behavior of laser-treated layer were systematically investigated to correlate their properties with process involved.
