Maria Clara Filippini Ierardi

Microstructural and hardness investigation of an aluminum-copper alloy processed by laser surface melting

Laser material processing has been widely applied in industrial processes due to the unique precision and very localized thermal action furnished by the lasers high energy density and power controllability. The scanned laser beam can be used to induce melting of a thin layer on metal surface when operated at higher intensity than that used for hardening. With the inherent rapid heating and cooling rates to which this surface layer is submitted, this process provides an opportunity to produce different microstructures from that of the bulk metal leading to useful properties. The major microstructural changes commonly observed in aluminum alloys are the extension of the solid solubility and the refinement of the microstructure. The objective of the current work was to analyze the microstructural and hardness variations throughout samples of an aluminum-copper alloy (Al-15 wt.% Cu) submitted to a laser surface remelting treatment. The analysis procedure consisted of scanning electron microscopy (SEM) characterization and microhardness tests in the resolidified and unmelted substrate regions.

The use of artificial intelligence technique for the optimisation of process parameters used in the continuous casting of steel

Abstract The productivity and quality of a continuous caster depend mainly on process parameters, i.e. casting speed, casting temperature, steel composition and cleanliness of the melt, water flow rates in the different cooling zones, etc. This work presents the development of an algorithm, which incorporates heuristic search techniques for direct application in metallurgical industries, particularly those using continuous casting process for the production of steel billets and slabs. This is done to determine the casting objectives of maximum casting rate as a function of casting constraints. These constraints are evaluated with the aid of a heat transfer and solidification model based on the finite difference technique, which has been developed and integrated with a genetic algorithm. The essential parts of continuous casting equipment, which must be subjected to monitoring, as well as a methodology of mathematical model and physical settlements in each cooling region, are presented. The efficiency of the intelligent system is assured by the optimisation of the continuous casting operation by maximum casting rate and defect-free products. This approach is applied to the real dimension of a steel continuous caster, in real conditions of operation, demonstrating that good results can be attained by using heuristic search, such as: smaller temperature gradients between sprays zones, reduction in water consumption and an increase in casting speed.

Surface Finishes for Ti-6Al-4V Alloy Produced by Direct Metal Laser Sintering

The implant’s surface is responsible for direct interaction with the human body. For cases where osseointegration must be favored and the risk of bacteria proliferation is lower, rough surfaces are more suitable, while for implants where the risks are higher, a reduced surface roughness is required. This study aimed to analyze and produce different surface finishes on samples of Ti-6Al-4V alloy produced by additive manufacturing technique of Direct Metal Laser Sintering (DMLS). Surfaces of the samples were analyzed in the as-built condition, after blasting, after chemical etching, after electropolishing and two different combinations of these methods. The surfaces were studied using the technique of scanning electron microscopy, and surface roughness and mass measurements. The lower roughness value was obtained after a combination of blasting and chemical etching. Blasting results in a surface with uniform roughness while chemical etching cleans the surface and reduces its roughness.

Mathematical modeling and experimental analysis of the hardened zone in laser treatment of a 1045 AISI steel

The aim of this work is to develop a mathematical model to predict the depth of laser treated zone in the LTH process. The Fourier equation of heat conduction is solved by using the Finite Difference Method in cylindrical coordinates in order to study the temperature distribution produced in a workpiece and hence to obtain the depth to which hardening occurs. The theoretical simulations are compared with results produced experimentally by a CO2 laser operating in continuous wave, showing good agreement.

Numerical and experimental analysis of laser surface remelting of Al–15Cu alloy samples

Abstract 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 and results of experiments of laser surface remelting of Al–15Cu samples, carried out in the present investigation, were used for validation of numerical simulations performed with the proposed model. The work also encompassed the analysis of microstructural parameters by scanning electron microscopy and microhardness variations throughout the resulting treated and unmolten zones.

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.

Thermal treatment effects on laser surface remelting duplex stainless steel

In this paper the microstructural changes and effects on corrosion resistance of duplex stainless steels UNS S32304 and UNS S32205, commonly used by the petroleum industry, were studied, following the execution of laser surface remelting (LSM) and post-thermal treatments (TT). In this way, data was obtained, which could then be compared with the starting condition of the alloys. In order to analyze the corrosion behaviour of the alloys in the as-received conditions, treated with laser and after post-thermal treatments, cyclic polarization tests were carried out. A solution of 3.5% NaCl (artificial sea water) was used, as duplex stainless steels are regularly used by the petroleum industry in offshore locations. The results obtained showed that when laser surface treated, due to rapid resolidification, the alloys became almost ferritic, and since the level of nitrogen in the composition of both alloys is superior to their solubility limit in ferrite, a precipitation of Cr2N (chromium nitrides) occurred in the ferritic matrix, causing loss of corrosion resistance, thus resulting in an increase in surface hardness. However, after the post-thermal treatment the alloys corrosion resistance was restored to values close to those of the as-received condition.

Numerical simulation and microstructural investigation of an aluminum-copper alloy processed by laser surface remelting

The aim of this work is to develop a mathematical model based on the finite difference method in order to simulate the remelting process. Good agreement between numerical and experimental results was obtained in the delimitation of the remelted zone. The work also concerns the analysis of the microstructural and hardness variations throughout samples of an aluminum-copper alloys (Al15 wt pct Cu) submitted to a laser surface remelting treatment. The specimens were examined by optical and scanning electron microscopy. Microhardness measurements were carried out on the transverse section for the resolidified and unmolten regions.