High-Strength Al-Zn-Cu-Based Alloy Synthesized by High-Pressure Die-Casting Method
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CONCLUSION
In this study, we synthesized Al-xZn-3Cu (x = 20, 30, 40 wt pct) alloys showing excellent mechanical properties. Considering that general Al alloys require melt modification and post-casting heat treatment, the findings may be summarized as follows: (1)
(2)
(3)
The size of the a-Al phase significantly decreases and the fraction of the hard phases such as an a+g and h increase with increasing Zn content. The increasing fraction of hard phases with increasing Zn content improved the hardness and strength of the developed die-casting alloys. The mechanical properties are drastically improved in the Al-Zn-based alloys by the increase of Zn addition. The Al-40Zn-based alloy exhibits an ultimate tensile strength of 435 MPa and an elongation of 3.8 pct without melt modification and post-casting heat treatment. The Vickers microhardness of the alloy also increases remarkably with increasing Zn content. Microscale study shows that the ultrafine Zn nanoprecipitations are uniformly distributed in
Fig. 8—(a) Z-contrast image of Al-40Zn-3Cu alloy recorded in grain boundary region with corresponding chemical maps for (b) Al, (c) Zn, and (d) Cu.
Fig. 9—(a) Bright-field image of Al-40Zn-3Cu alloy. (b) Experimental CBED pattern is recorded from the Zn phase and compared to (b) the simulated CBED pattern. (c) The magnified bright-field image of the region II with (d) corresponding spot electron diffraction pattern.
(4)
the primary Al grain, resulting in the incoherent strain along {1 10}. The Zn addition induces very complex microstructure in the developed Al-xZn-3Cu alloys. The unique microstructure of Al-xZn-3Cu alloys is considered to be a key to absorb the deformation energy.
Based on the above, we consider that the improved strength is attributed to fine a-Al grains with Zn nanoprecipitations, and also the complex grain boundary structure, which has very fine Al and Zn phases, as well as other phases.
METALLURGICAL AND MATERIALS TRANSACTIONS A
Table VII. Mechanical Properties of Non-Heat-Treatable Al Alloys and of Developed Al-xZn-3Cu Alloys Alloy
Tensile Strength (MPa)
Al-20Zn-3Cu Al-30Zn-3Cu Al-40Zn-3Cu AA3003 AA3003 AA4015
~ ~ 110 to ~ 270 to ~
AA5083
349 397 435 133 180 150 180 345 317
Elongation (Pct)
Temper
4.3 4.1 3.8 ~ 7.5 ~4 ~ 20 ~2 ~ 12 ~ 16
— — — — H18 O H18 O/H111 H116
Fig. 10—3D tomography of HPDC Al-40Zn-3Cu alloy with volume of each phase; images show the (a) a-Al in a+g, (b) g in a+g, (c) a+g, (d) a-Al of grain, and (e) h phase of Al-40Zn-3Cu alloy sample (size of 20 x 25 x 25 lm).
ACKNOWLEDGMENTS The authors appreciate Young-Woo Jeong, Dr. Young-Woon Byeon, and Dr. Jae-Pyoung Ahn from Advanced Analysis Center, Korea Institute of Science and Technology, for their support of the 3D tomography analysis. This work was supported by the Regional Specialized Industry Development Program (Project No: R0006348), the Civil-Military Technology Cooperation Program (Project No: 18-CM-MA-16), and also partially supported by the R&D program of Korea Institute of Industrial Technology.
REFERENCES 1
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