June 13, 2014 To: Paul C. Lynch From: Group D Subject: Lab 6 Solidification Curves (Executive Memo) Dear Paul: It is always important to be knowledgeable of any materials being used in a casting because different materials yield different mechanical properties of the final product. However, most metal products are not in their pure form, but are actually a mixture of two or more metals, termed an alloy. Altering the compositions of the metals within an alloy, can drastically impact the mechanical and physical properties. This being said, it is necessary to know the general composition of the alloy that is being used. Each alloy has its own solidification signature. The transformation from liquid to solid involves a phase change, and the melting point of a metal is the temperature in which the solid and liquid phases can exist in equilibrium. The use of solidification cooling curves is a powerful technique for rapidly estimating alloy composition and melt quality. The inflection points of the temperature vs. time plots can be used to determine alloy composition. For simple alloys, such as Sn­Pb solder alloys, interpretation of the cooling curve is straight forward. Each alloy has a characteristic liquidus and solidus temperature that can be estimated from the cooling curve. This liquidus temperature can then be used with the Tin­Lead Temperature Equilibrium Phase Diagram to determine the corresponding compositions of each alloy. The objective of this lab is to determine the melting point temperature of solder alloys by plotting solidification cooling curve graphs, and to use these findings to also determine the tin and lead compositions of each alloy. In order to construct a solidification cooling curve for each alloy, its temperature must be recorded at a constant rate while it cools. To begin, an alloy of an unknown composition, labeled A, is initially weighed and then heated to 750​
°​
, using a thermocouple to check the temperature. . This crucible and thermocouple are then transferred to an insulated beaker and covered with ceramic wool insulation. Once the temperature had reached 700​
°F, temperature readings were taken every 30 seconds until the temperature had dropped to 300°F. It was important to ensure that the thermocouple was submerged in the alloy for the entirety of the cooling. This process was repeated for other unknown alloys, B, C, D, E, and F. When all the data was collected, cooling curves were constructed, using Microsoft Excel, and then analyzed for further evaluation. EVALUATION: Sample A, there was a change in slope at 408° F and then again at 366° F. The line was very shallow sloped, so this meant that there was a higher amount of Tin than Lead. By using these temperatures and relating them to Figure 4 we determined the different compositions. Sample B, did not have a slope, so therefore it was either a pure metal or the eutectic point. due to the temperature of the change around 370° F it was determined to be the eutectic composition. Sample C and D, both showed a change in slope at around 450° F but were very small. Because of this, both samples were mostly pure Tin. Sample E showed a change in slope at 520​
° ​
F​
​
and​
​
366​
° ​
F in Figure 4 this corresponded to a composition of 27% Tin and 73% Lead. Sample F showed a change in slope at 443​
° ​
F and 367° F in Figure 4 this corresponded to a composition of 91% Tin and 9% Lead. Overall, the compositions with the lowest heat changes had the fastest cooling rates. These corresponded to the compositions closest to the pure metals as well as the eutectic point. Specific samples B,D, and E show the fastest cooling rate. Figure 1: Cooling Curve for A&B Figure 2: Cooling Curve for C&D Figure 3: Cooling Curve for E&F Figure 4: ​
Tin­Lead Temperature Equilibrium Phase Diagram Part D: Composition/ Heat Release/ Melting Points Data Table (During Phase Change) Estimated Sample mass (g) A Composition Phase Change Liquidus Solidus Q (cal) Temp (T​
) L​
Temp (T​
) S​
%Sn %Pb 150g. 80 20 1929 408 366 B 150g. 61.9 38.1 1706.37 379 369 C 150g. 95 5 2113.5 452 453 D 150g. 93 7 2088.9 445 429 E 150g. 27 73 1277.1 520 366 F 150g. 91 9 2064.3 443 367 Calculations for the change of phase: A­ Q(cal) = (120)(14.5)+(30)(6.3) = 1929 cal B­ Q(cal) = (92.85)(14.5)+(57.15)(6.3) = 1706.37 cal C­ Q(cal) = (142.5)(14.5)+(7.5)(6.3) = 2113.5 cal D­ Q(cal) = (139.5)(14.5)+(10.5)(6.3) = 2088.9 cal E­ Q(cal) = (40.5)(14.5)+(109.5)(6.3) = 1277.1 cal F­ Q(cal) = (136.5)(14.5)+(13.5)(6.3) = 2064.3 cal Part E: Composition/ Heat Release/ Melting Data Table (Total From 700F to 300F; 371C to 150C) Sample mass (g.) Estimated Composition Total Liquidus Solidus %Sn %Pb Q (cal) Temp (T​
) L​
Temp (T​
) S​
3753.3 408 366 A 150g. 80 20 B 150g. 61.9 38.1 3381.67 379 369 C 150g. 95 5 4061.33 452 453 D 150g. 93 7 2376.36 445 429 E 150g. 27 73 2665.05 520 366 F 150g. 91 9 3979.19 443 367 Calculations for the total change : A­ Q(cal) = [(120)(0.053)(120)+(120)(0.063)(25)+(120)(0.071)(75)]+[(30)(0.0335)(13)+(30)(0.038)(65)+(3
0)(0.03312)(50)+(30)(0.03243)(50)+(30)(0.03176)(50)]+[1929]= 3753.3 cal B­ Q(cal) = [(92.85)(0.053)(120)+(92.85)(0.063)(25)+(92.85)(0.071)(75)]+[(57.15)(0.0335)(13)+(57.15)(0.
038)(65)+(57.15)(0.03312)(50)+(57.15)(0.03243)(50)+(57.15)(0.03176)(50)]+[1706.37]= 3381.67 cal C­ Q(cal) = [(142.5)(0.053)(120)+(142.5)(0.063)(25)+(142.5)(0.071)(75)]+[(7.5)(0.0335)(13)+(7.5)(0.038)(
65)+(7.5)(0.03312)(50)+(7.5)(0.03243)(50)+(7.5)(0.03176)(50)]+[2113.5]= 4061.33 cal D­ Q(cal) = [(139.5)(0.053)(120)+(139.5)(0.063)(25)+(139.5)(0.071)(75)]+[(10.5)(0.0335)(13)+(10.5)(0.03
8)(65)+(10.5)(0.03312)(50)+(10.5)(0.03243)(50)+(10.5)(0.03176)(50)]+[2088.9]= 2376.36 cal E­ Q(cal) = [(40.5)(0.053)(120)+(40.5)(0.063)(25)+(40.5)(0.071)(75)]+[(109.5)(0.0335)(13)+(109.5)(0.038)
(65)+(109.5)(0.03312)(50)+(109.5)(0.03243)(50)+(109.5)(0.03176)(50)]+[1277.1]= 2665.05 cal F­ Q(cal) = [(136.5)(0.053)(120)+(136.5)(0.063)(25)+(136.5)(0.071)(75)]+[(13.5)(0.0335)(13)+(13.5)(0.03
8)(65)+(13.5)(0.03312)(50)+(13.5)(0.03243)(50)+(13.5)(0.03176)(50)]+[2064.3]= 3979.19 cal Sincerely, Group D Jake Stanko(10), Prithvi Doddanavar(4), Kate Gilland(6), Kaushal Pathak(9)