Table 1. Impact of Height Above the Chill on the Properties of 6061 0 mm 10 mm 18 mm 25 mm
Ultimate tensile strength (MPa) Yield strength (Mpa) Elongation (%)
Table 2. Impact of Homogenizing Time on the Properties of 6061
Ultimate tensile strength (MPa)
6 hrs 12 hrs 369
370
Yield strength (Mpa) 334 Elongation (%)
7.2
331 7.7
385 340 9.6
373 332 8.9
364 335 5.6
Table 3. Impact of Iron level on the Properties of 6061
Ultimate tensile strength (MPa)
0.10% 0.15% 368
372
Yield strength (Mpa) 331 Elongation (%)
7.2
339 7.5
Table 4. Impact of Height Above the Chill on the Properties of 6082 0 mm 10 mm 18 mm 25 mm
Ultimate tensile strength (MPa) 390.52 Yield strength (Mpa) Elongation (%)
Table 5. Impact of Homogenizing Time on the Properties of 6082
Ultimate tensile strength (MPa)
6 hrs 12 hrs 372
375
Yield strength (Mpa) 343 340 Elongation (%)
4.6 2 Procedure
T e study tested vari- ants of the 6061 wrought alloy (without copper) and variants of the 6082
wrought alloy. “T e main objective was to study
the [iron] phase formation and dis- solution at two [iron] levels, over a range of freezing rates, and as a function of time and temperature for the [heat treating] parameters,” the researchers wrote. Each alloy confi guration was cast into duplicate end-chilled blanks. T e fi rst blank was dissected and heat treated at various times and tempera- tures for metallographic study. T e second was sliced and heat treated
5.8 373.77
346.15 340.09 8.85
5.43
370.67 345.01 3.82
358.88 334.25 2.85
Table 6. Impact of Iron Level on the Properties of 6082
Ultimate tensile strength (MPa)
0.10% 0.15% 374
373
Yield strength (Mpa) 339 Elongation (%)
5.8
344 4.6
before being tested for diff erences in mechanical properties. T e experiment also involved a
chemistry and hot tearing study in which the researchers added titanium and other elements to the two base al- loys to determine the best addition for the reduction of hot tear defects in the fi nal castings. Two casting processes, semi-solid casting and fully liquid diecasting, were examined to deter- mine which was the most eff ective in producing defect-free castings.
3
Results and Conclusions
The study of the as-
cast microstructure of the two alloy families showed
46 | METAL CASTING DESIGN & PURCHASING | Jan/Feb 2012
354.36 321.79 5.7
significant differences between the iron phases encountered in 6061 and those in 6082, with respect to their distance from a chill. (A chill is a metal insert used in a casting mold to induce rapid solidification of certain pockets of metal. In this situation, the chill is the bottom of the copper mold. Because the mold sides are composed of sand, a major- ity of the heat is drained through the bottom.) The differences still were significant after six hours of heat treating at 986F (530C) and 1,058F (570C) (Figs. 1 and 2). A comparative image analysis was
performed between 0.1 and 0.15% iron contents in the alloys, with ho- mogenizing time for the 6061 variants. T e researchers said the plots showed little advantage was gained from the 24-hour homogenizing time compared to the 12-hour time in terms of mean or maximum iron phase length. T e 24-hour soak also resulted in a phe- nomenon known to reduce toughness in wrought 6061. T e mechanical property study also
analyzed diff erences with respect to the chill for both alloy families. T e infl uence of three diff erent variables is reported in Tables 1-6. In the hot tearing and chemistry
study, the researchers observed that adjustment of the chemical com- position and the use of appropriate alloy additions can result in a hot tearing index lower than expected for the base alloy. They reported semi-solid casting produced a lower hot tear index compared to con- ventional diecasting for most 6000 series alloys. The study indicated mechani-
cal properties exhibiting both high ductility and strength can be achieved in a cast product. Further optimization via heat treatment may be possible, the researchers said, and the casting process used is critical to the success of the alloys’ production. Emerging casting processes like the ablation process (in which water is used to strip a sand mold away during cooling to achieve elevated microstructure) have shown little tendency towards hot tearing. T e researchers indicated the
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