Thiago A. Costa

Solidification thermal parameters and dendritic growth during the horizontal directional solidification of Al-7wt.%Si alloy

O principal objetivo desse trabalho e investigar a influencia dos parâmetros termicos velocidade de solidificacao (VL) e taxa de resfriamento (TR), nos espacamentos dendriticos primarios (λ1) da liga hipoeutetica Al-7%Si, durante a solidificacao direcional horizontal, em regime transiente. Os valores de λ1 foram medidos ao longo do comprimento do lingote e correlacionados com esses parâmetros. A variacao dos espacamentos dendriticos estudados e expressa por meio de funcoes na forma de potencia de VLe TRdadas, respectivamente, por λ1= 55(VL)-1.1e λ1= 212 (TR)-0.55. Um estudo comparativo e realizado entre os resultados encontrados nesse trabalho e aqueles obtidos para a mesma liga quando solidificada direcionalmente nos sistemas verticais ascendente e descendente, sob as mesmas condicoes assumidas. Finalmente, os resultados experimentais obtidos sao comparados com valores fornecidos por alguns modelos teoricos propostos na literatura para analisar espacamentos dendriticos primarios.

Interconnection between microstructure and microhardness of directionally solidified binary Al-6wt.%Cu and multicomponent Al-6wt.%Cu-8wt.%Si alloys

An experimental study has been carried out to evaluate the microstructural and microhardness evolution on the directionally solidified binary Al-Cu and multicomponent Al-Cu-Si alloys and the influence of Si alloying. For this purpose specimens of Al-6wt.%Cu and Al-6wt.%Cu-8wt.%Si alloys were prepared and directionally solidified under transient conditions of heat extraction. A water-cooled horizontal directional solidification device was applied. A comprehensive characterization is performed including experimental dendrite tip growth rates (VL) and cooling rates (TR) by measuring Vickers microhardness (HV), optical microscopy and scanning electron microscopy with microanalysis performed by energy dispersive spectrometry (SEM-EDS). The results show, for both studied alloys, the increasing of TR and VL reduced the primary dendrite arm spacing (l1) increasing the microhardness. Furthermore, the incorporation of Si in Al-6wt.%Cu alloy to form the Al-6wt.%Cu-8wt.%Si alloy influenced significantly the microstructure and consequently the microhardness but did not affect the primary dendritic growth law. An analysis on the formation of the columnar to equiaxed transition (CET) is also performed and the results show that the occurrence of CET is not sharp, i.e., the CET in both cases occurs in a zone rather than in a parallel plane to the chill wall, where both columnar and equiaxed grains are be able to exist.

Influência das Variáveis Térmicas Sobre os Espaçamentos Dendríticos Terciários durante a Solidificação Direcional Horizontal da Liga Al-6%Cu

A liga Al-6%Cu foi solidificada direcionalmente sob condicoes transitorias de extracao de calor e microestruturas dendriticas, variaveis termicas de solidificacao, ou seja, velocidade de deslocamento da isoterma liquidus (VL), taxa de resfriamento (TR) e gradiente de temperatura a frente da isoterma liquidus (GL) foram caracterizadas, determinadas experimentalmente e correlacionadas com os espacamentos dentriticos terciarios (λ3). Para tanto, foi projetado, construido e aferido um dispositivo de solidificacao direcional horizontal. Os resultados encontrados mostram que leis de potencia -1,1 e -0,55 caracterizam a variacao dos espacamentos terciarios com a velocidade de deslocamento da isoterma liquidus (VL) e a taxa de resfriamento (TR), respectivamente. Finalmente, e realizado um estudo comparativo entre os resultados obtidos neste trabalho e aqueles publicados na literatura para ligas Al-Cu solidificadas direcionalmente sob condicoes transientes de fluxo de calor nos sistemas verticais ascendente e descendente.

Aplicação de prensas de rolos em minério de ferro

The Minas-Rio Project that is being implemented by Anglo Ferrous Brazil, foresees the use of HPGR (High Pressure Grinding Rolls) to grind the undersize from screening at (-25.4 mm). This application is recent for iron ore comminuting. The study described herein, took place at the Krupp/Polysius Research Center, in Germany, aiming to validate the HPGR application for iron ore, as well as to determine the main parameters used in equipment sizing. The study also aimed to assesses the impact of moisture variation on ore feed in respect to specific grinding capacity and product size distribution. The great results obtained from the sample tests that demonstrated more process stability for the work index (wi) and granulometric feed distribution variations, together with the possible financial gains from the HPGR implementation, contributed to the unrestricted approval of the HPGR application for iron ore comminuting in the Minas-Rio Project.

Tailoring Morphology and Size of Microstructure and Tensile Properties of Sn-5.5 wt.%Sb-1 wt.%(Cu,Ag) Solder Alloys

Transient directional solidification experiments, and further optical and scanning electron microscopy analyses and tensile tests, allowed the dependence of tensile properties on the micromorphology and length scale of the dendritic/cellular matrix of ternary Sn-5.5Sb-1Ag and Sn-5.5Sb-1Cu alloys to be determined. Extensive ranges of cooling rates were obtained, which permitted specific values of cooling rate for each sample examined along the length of the casting to be attributed. Very broad microstructural length scales were revealed as well as the presence of either cells or dendrites for the Ag-containing alloy. Hereafter, microstructural spacing values such as the cellular spacing, λc, and the primary dendritic spacing, λ1, may be correlated with thermal solidification parameters, that is, the cooling rate and the growth rate. While, for the Cu-containing Sn-Sb alloy, the β-Sn matrix is characterized only by the presence of dendritic arrangements, the Ag-containing Sn-Sb alloy is shown to have high-velocity β-Sn cells associated with high cooling rate regions, i.e., positions closer to the bottom of the alloy casting, with the remaining positions being characterized by a complex growth of β-Sn dendrites. Minor additions of Cu and Ag increase both the yield and ultimate tensile strengths when compared with the corresponding values of the binary Sn-5.5Sb alloy, with a small reduction in ductility. This has been attributed to the homogeneous distribution of the Ag3Sn and Cu6Sn5 intermetallic particles related to smaller λ1 characterizing the dendritic zones of the ternary Sn-Sb-(Cu,Ag) alloys. In addition, the Ag-modified Sn-Sb alloy exhibited an initial wetting angle consistent with that characterizing the binary Sn-5.5Sb alloy.

Correlation between Thermal Parameters, Primary Dendrite Arm Spacing and Microhardness on a Directionally Solidified Ternary Al-6wt%Cu-8wt%Si Alloy

The objective of this paper is to present an experimental study that aimed to establish correlations between primary dendrite spacing (λ1) and microhardness of a ternary Al-6wt%Cu-8wt%Si alloy solidified under transient heat extraction, using a horizontal unidirectional water-cooled solidification device. To examine the microstructural evolution, solidification thermal parameters (growth rate and cooling rate - VL and TR, respectively) were calculated through the application of an experimental method and were then correlated with λ1 using analytical power functions laws. The correlation between microstructural parameters and the measured microhardness values are presented in the forms of power and Hall-Petch types of equations. The analysis of the microstructure of the investigated alloy indicated that the increasing of TR and VL reduced the primary dendrite arm spacing, increasing the microhardness.