Table 4.7 indicates the effect of heat treatment on the percentage elongation and ultimate tensile strength of silicon bronzes
Table 4.7: Effect of heat treatment on the percentage elongation and ultimate tensile strength of silicon bronzes
Alloy composition Condition UTS (MPa) %E Cu-3wt%Si-3wt%Zn non-heat treated 353 17.4 Cu-3wt%Si-3wt%Zn heat treated 376 13.4 Cu-3wt%Si-3wt%Sn non-heat treated 238 11.1 Cu-3wt%Si-3wt%Sn heat treated 229 11.8 Cu-3wt%Si-0.8wt%Mg non-heat treated 285 19.1 Cu-3wt%Si-0.8wt%Mg heat treated 306 16.3 Cu-3wt%Si-1wt%Mn non-heat treated 378 6.5 Cu-3wt%Si-1wt%Mn heat treated 385 5.4 Cu-3wt%Si-0.8wt%W non-heat treated 286 20.8 Cu-3wt%Si-0.8wt%W heat treated 298 15.6 Cu-3wt%Si-2wt%Ti non-heat treated 265 7.2 Cu-3wt%Si-2wt%Ti heat treated 274 5.8 Cu-3wt%Si-1.5wt%Mo non-heat treated 130 12.1 Cu-3wt%Si-1.5wt%Mo heat treated 168 10.8 Cu-3wt%Si-3wt%Al non-heat treated 314 5.1 Cu-3wt%Si-3wt%Al heat treated 322 3.4
The percentage elongation of heat treated and non-heat treated silicon bronze is presented in Figure 4.39. Analysis of Figure 4.39 indicates that heat treatment significantly decreased the percentage elongation of silicon bronze doped with Zn, Mg, Mn, W, Ti, Mo and Al. This change is quantified by the existence of refined and coherent intermetallic compound in the alloy structure. The alloy doped with tin showed different behavior.
97
Figure 4.39: Effect of heat treatment on the percentage elongation of silicon bronzes.
Figure 4.40 shows the effect of heat treatment on the ultimate tensile strength of silicon bronzes. Analysis of Figure 4.40 shows increase in ultimate tensile strength of heat treated alloy doped with Zn, Mg, Mn, W, Ti, Mo and Al. This could be attributed to decrease in grain size and increase in distribution of the intermetallic compound in the copper matrix. Alloy doped with Sn showed different effect as a result of formation of non-coherent intermetallic compound in the alloy structure as evidenced in the microstructural analysis.
0 5 10 15 20 25
Percentage elongation (%E)
Alloys compositions
non-heat treated Heat treated
98
Figure 4.40: Effect of heat treatment on the ultimate tensile strength of silicon bronzes.
The effect of heat treatment on the hardness and impact strength of silicon bronzes is presented in Table 4.8. This table shows the comparison between the ultimate tensile strength of heat treated and non-heat treated silicon bronzes.
0 50 100 150 200 250 300 350 400 450
Ultimate tensile strength (MPa)
Alloys compositions
non-heat treated Heat treated
99
Table 4.8: Effect of heat treatment on the hardness and impact strength of silicon bronzes
Alloy composition Condition Brinell hardness (MPa) Impact strength (J) Cu-3wt%Si-3wt%Zn non-heat treated 254 24.4
Cu-3wt%Si-3wt%Zn heat treated 268 19.5 Cu-3wt%Si-3wt%Sn non-heat treated 278 25.2 Cu-3wt%Si-3wt%Sn heat treated 251 25.9 Cu-3wt%Si-0.8wt%Mg non-heat treated 318 13.2 Cu-3wt%Si-0.8wt%Mg heat treated 387 10.4 Cu-3wt%Si-1wt%Mn non-heat treated 371 8.3 Cu-3wt%Si-1wt%Mn heat treated 390 5.3 Cu-3wt%Si-0.8wt%W non-heat treated 358 16.6 Cu-3wt%Si-0.8wt%W heat treated 364 12.8 Cu-3wt%Si-2wt%Ti non-heat treated 282 10.2 Cu-3wt%Si-2wt%Ti heat treated 308 9.3
Cu-3wt%Si-1.5wt%Mo non-heat treated 192 8.5 Cu-3wt%Si-1.5wt%Mo heat treated 201 6.8 Cu-3wt%Si-3wt%Al non-heat treated 278 14.2 Cu-3wt%Si-3wt%Al heat treated 284 10.4
The hardness of silicon bronze solution heat treated at temperature of 900oC for 30 minutes and cooled in air is presented in Figure 4.41. This figure shows that heat treatment significantly improved the hardness of silicon bronzes doped with Zn, Mg, Mn, W, Ti, Mo and Al. The observed increase in hardness could be attributed to the decrease in grain size and increase in distribution pattern of the intermetallic compound. Alloy doped with Sn showed decreased hardness when subjected to solution heat treatment.
100
Figure 4.41: Effect of heat treatment on the hardness of silicon bronzes.
Figure 4.42 shows the effect of solution heat treatment on the impact strength of silicon bronze doped with Zn, Mg, Mn, W, Ti, Mo and Al. Figure 4.42 shows that the impact strength of silicon bronze doped with zinc, magnesium, manganese, titanium and aluminium decreased significantly when subjected to heat treatment. Silicon bronze doped with tin showed increase in impact strength when heat treated (Figure 4.42).
0 50 100 150 200 250 300 350 400 450
Brinell hardness (MPa)
Alloys compositions
non-heat treated Heat treated
101
Figure 4.42: Effect of heat treatment on the impact strength of silicon bronzes.
4.1.2 Effect of heat treatment on the physical properties of the best alloys