Aluminium alloys are subject of continuous variations in their composition due to the permissible range of tolerance for the elements in their chemical composition as well as natural changes such as a loss of Mg during the foundry process. The usual additives of treatment products, whose effect are marginally stable can also alter the solidification conditions.
Further consider the use of recycled material, which is daily practice in almost every foundry, you can realize that ideal theoretical curves, zero-lines, set values etc. cannot be valid. Only by recording the actual solidification characteristic a true analysis can be performed. To consider the "modified condition" of the melts as "0" or totally unmodified before addition of the modifying treatment, like tablets etc. isn't proper.
To evaluate the actual modification it is necessary to distinguish between the effect on the depression of the eutectic point as a result of the alloying elements such as Mg, Cu , Fe etc. on the one hand and the modifying elements Na, Sr, Sb etc. on the other hand. Only then it is possible to analyse which elements are involved and how strong their influence is on the solidification process. In short: Depression is not the same as Modification.
These effects on the solidification process dependend on the effect of the available quantity: A glance through reference literature shows for example that every 0.1% Mg can cause a ΔT of 0.8 - 1.2 K; that means in an LM25 where the Mg level should be between 0.25 and 0.45% the average of 0.3% Mg could cause a ΔT of 2.4 - 3.6 K. Consider not to forget that 4.5 K is the maximum depression which can be achieved by Sr. For this reason it is more important to determine the effect than the amount. A modification for example depends on the effect of Na, Sr and/or P, Ca etc. It is not true that, because a modifying element is quantitatively present that a modification has already been achieved.
A precise recording of the solidification and a distinguished analysis, i.e. determination of all influences involved, is the fundamental condition for proper assessment of modification / grain refining. Today all of these findings are an integral part of TA-System 748, so that a full-automatic analysis is possible.
The results of the complete documentation, in summary on a protocol wich informes in detail about suppliers of the materials, melt process, melting treatment, results of the accompanying examination to infer temperature gradient as well as goal and identification of cast parts is the represented typical printout of a TA-748. Of course the TA-748 has a central cross-linkable database, in wich all information, incl. external measuring data e.g. spectral, temperatures, VAC-TEST etc. ..., are automatically stored and administrated . The use of such database approximately for the analysis of dependencies and statistics of a kind is nearly unlimited, because of the individual design.