Another interesting observation is that HIPing not only improves the elongation (as usual, by removing whatev- er microporosity was present in the test-bars), but also tends to “soften” the alloy. The TYS is systematically reduced by 5 MPa along the plateau, and the difference is amplified in the zone of steep variation at 0.07%.
At Cu 4.0% a plateau of properties is observed be- tween Mg 0.10% and 0.20%, similarly to what has been seen at Cu 3.5% (See Figure 7). Consequently, no Cu – Mg interaction seems to exist in this narrow domain and it has been possible to average the prop- erties along each plateau. The various lines (black for non-HIPed, dotted gray for HIPed, blue for the softer HIPed alloy at Mg = 0.07%) show the effect of Cu between 3.5% and 4.0%, which we believe can safely be extrapolated downwards at least to 3.2%. As could be expected, Cu effectively hardens the alloy and re- duces its ductility.
250C (482F) and 300C (572F) Tensile Properties: Influences of Mg and Cu: They have been measured only in the non-HIPed condition. The results reported here (Figure 8) are those obtained with the conditions of EN 10 002-5 (reference “NLV” in this work). A comparison with the former norm EN 10 002-1 (used in previous works)1,2
has been run on the same series
of samples (Mg 0.10 – 0.20). The two norms differ in the rate of deformation, which is much lower in the recent EN 10 002-5: 0.004 min-1 and 0.1 min-1 1 and 0.2 min-1 10 002-1.
in the elastic range
in the plastic range, as against 0.05 min- respectively in the formerly used EN
These results fit well with those of phase 1 and show that the plateau observed between Mg 0.10% and 0.20% also applies to elevated temperature properties. They also confirm that HIPing slightly softens this alloy type: see the superposition of phase 1 HIPed and phase 2 non- HIPed results around Mg 0.10%.
Remarkably, is that the effect of Cu between 3.5% and 4.0%, very notable at room tempera- ture, dwindles with increasing temperature and becomes nil at 300C, instead of increasing in rela- tive terms as could have been expected (Figure 9).
Effect of the Deformation Speed in the Ten- sile Testing: UTS and elongation are little (not significantly in these tests) affected, but the TYS values afforded by the new, slower rate of traction of EN 10 002-5 are lower by 6% at 250C (482F) and 10% at 300C.
Effect of Iron on the Tensile Properties: It has been measured in a Mg 0.15%, Cu 3.5% batch in which the Fe has been raised to 0.18%. Its prop-
International Journal of Metalcasting/Summer 2011
Figure 6. Effect of Mg and HIP between 0.00% and 0.20% on the room temperature properties at Cu 3.5%.
21
erties at room temperature, 250C (482F) and 300C (572F) have been compared with the average “plateau” values cor- responding to Fe 0.10%. As could be expected, at room temperature, the TYS is unaffected and the UTS only very slightly affected, but the elongation decreases by one- third. At 250C (482F) and 300C (572F) (see the violet points in the above figures), the embrittling effect is much less due to the softness of the matrix.
Figure 4. 250C (482F) properties at Mg 0.00%, 0.05% and 0.10%.
Figure 5. 300C (572F) properties at Mg 0.00%, 0.05% and 0.10%.
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