Detection of Dendrite Coherency Temperature of Aluminum Alloys Using Single Thermocouple Technique

Abstract

The dendrite coherency point (DCP) temperature refers to the state of a solidifying alloy at which a coherent dendrite network is established during the formation of grains. There are three main approaches for detection of DCP: (i) the thermal analysis method, (ii) mechanical (or rheological) technique and (iii) physical method based on the thermal diffusivity measurement technique.There are two basic variants of the thermal analysis method. In the late 1980's Bäckerud developed a method that utilizes two thermocouples. The DCP is determined by identifying the point of minimum temperature difference at the δT curve (TW–TC). Recently, has been revealed that utilization of the first derivative curve (dT/dt) plotted versus temperature also allows for analysis of the α-Al dendrite nucleation and growth characteristics and consequently determination of the DCT. This paper will illustrate that the dendrite coherency temperature could be identified by the 1st derivative curve (the one-thermocouple method) with the same accuracy as well as by using two thermocouples technique.

Review of thermal analysis applications in aluminium casting plants

“…The available literature provides a few others methods that have been used to detect this parameter. Jiang et al (1999), Djurdjevic et al (2012a) and Djurdjevic et al (2001b) used one (Tc) thermocouple located in the centre of the TA cup to determine the DCP temperature characteristics. The DCP is defined as the minimum point on the second derivative curve.…”

Quantification of Feeding Regions of Hypoeutectic Al-(5, 7, 9)Si-(0-4)Cu (wt.%) Alloys Using Cooling Curve Analysis

“…In addition, Cu reduces the corrosion resistance of aluminum alloys, and in certain alloys increases stress corrosion susceptibility. This element is generally responsible for reducing the casting characteristics, especially the feeding ability of Al-Si-Cu alloys [8][9][10].…”

“…There is a lack of data, in the available literature, regarding quantification of feeding regions. The objective of this work is to examine how variation in chemical composition of Al- (5,7,9) Si-(0-4)Cu (wt.%) alloy may affect its characteristic solidification temperatures and corresponding fraction solid related to each temperature, as well as to quantify the effect of various contents of Si and Cu on the corresponding feeding regions. This analysis should help foundry professionals to understand better which feeding regions are more responsible for the formation of shrinkage porosity.…”

Effect of Si and Cu concentrations and solidification rate on soundness in casting structure in Al–Si–Cu alloys

“…[29][30][31] Under unmodified conditions (Sr near residual, e.g. (20 ppm), the Al-Si begins to nucleate from the dendrite surfaces and the Al-Si solid/ liquid interface advances into interdendritic regions.…”