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A study was conducted to examine the effect of solidification time and solution treatment time on the tensile properties of a 319-type aluminum alloy. Tensile samples with solidification times ranging from 0.3 to 35.5 minutes were solution-treated at 495 C for 8 hours and for 240 hours. All samples were then water-quenched and aged at 260 C for 4 hours. The tensile results show that solidification time and solution treatment time can have significant effects on the tensile properties. In general, as the solidification time increased, the ultimate strength, yield strength, and ductility decreased; increasing the solution-treatment time from 8 to 240 hours improved only the tensile strengths. The amount of Cu available in solid solution to precipitate during aging is found to be a key factor. Additionally, coarse microstructures require very long (and commercially-impractical) solution-treatment times to significantly improve the tensile strengths.

New high-temperature Mg alloys are being considered to replace 380 Al in transmission cases, wherein bolt-load retention, and creep, is of prime concern. One of these alloys is die cast AE42, which has much better creep properties than does AZ91D but is still not as creep resistant as 380 Al. It is thus important to investigate bolt-load retention and creep of AE42 as an initial step in assessing its suitability as a material for transmission housings. To that end, the bolt-load retention behavior of die-cast AE42, AZ91D and 380 Al have been examined using standard M10 bolts specially instrumented with stable high-temperature strain gages. The bolt-load retention test pieces were die cast in geometries approximating the flange and boss regions in typical bolted joints. Bolt-load retention properties were examined as a function of time (at least 100 hours), temperature (150 and 175 °C) and initial bolt preload (14 to 34 kN).

The recent development of TiAl-based alloys by the aerospace community has provided an excellent material alternative for hot components in automotive engines. The low density combined with an elevated temperature strength similar to that of Ni-base superalloys make TiAl-based alloys very attractive for exhaust valve applications. Lighter weight valvetrain components improve performance and permit the use of lower valve spring loads which reduce noise and friction and enhance fuel economy. However, difficult fabricability and a perception that TiAl alloys are high cost, low volume aerospace materials must be overcome in order to permit consideration for use in high-volume automotive applications. This paper provides a comparison of properties for several exhaust valve alternative materials. The density of TiAl alloys is lower than Ti alloys with creep and fatigue properties equivalent to IN-751, a current high performance exhaust valve material.

Titanium alloys offer a unique combination of high strength-to-weight ratio, good corrosion resistance and favorable high temperature mechanical properties. While the high cost of titanium has severely restrained consideration of titanium usage in mass produced automobiles, there are certain components for which titanium alloys are particularly well suited from a design viewpoint. The most promising of these applications include suspension springs and engine components such as valves, valve springs and valve retainers. The technical advantages offered by the use of titanium alloys in these applications include reductions in vehicle weight and improvements in performance, fuel economy and packaging efficiency. This paper reviews characteristics of the several types of titanium alloys.