In this work, the effect of thermal exposure on high temperature mechanical properties of secondary AlSi7Cu3Mg foundry alloys has been studied as a function of ageing time. The alloy was solution treated at 485 °C for 24 h, water quenched and aged at 180 °C for times ranging from 1 to 10 h. The hardness of the as-quenched alloy is ~84 HB and it stabilizes at ~135 HB after ageing. The aged specimens were then soaked at 200 and 300 °C for 1 h and tested at high- and room-temperature by means of hardness measurements. At 200 and 300 °C the hardness values generally reduce to about 110 and 42 HB, respectively. The severe hardness decreases at 300 °C is attributed to the combined effect of α-Al phase softening and coarsening of the strengthening precipitates. After 200 °C exposure and room-temperature testing, hardness values are equal to the unexposed material, while after 300 °C exposure and room-temperature testing the average hardness reduces to ~80 HB due to the evolution of reinforcing needle-like phase (presumably β'' or β' phase) toward coarser platelet-like θ' precipitates. Finally, as the hardness measurements at high- and room-temperature show almost constant values for each exposure condition, exposing the specimens at 200 °C and 300 °C for 1 h makes the effect of ageing treatment vanish for ageing times longer than 1 h.
Influence of T6 heat treatment on secondary AlSi9Cu3(Fe) alloy produced by semi-solid seed process
Fabrizi A.
Writing – Original Draft Preparation
;Timelli G.Funding Acquisition
;De Mori A.Writing – Review & Editing
2018
Abstract
In this work, the effect of thermal exposure on high temperature mechanical properties of secondary AlSi7Cu3Mg foundry alloys has been studied as a function of ageing time. The alloy was solution treated at 485 °C for 24 h, water quenched and aged at 180 °C for times ranging from 1 to 10 h. The hardness of the as-quenched alloy is ~84 HB and it stabilizes at ~135 HB after ageing. The aged specimens were then soaked at 200 and 300 °C for 1 h and tested at high- and room-temperature by means of hardness measurements. At 200 and 300 °C the hardness values generally reduce to about 110 and 42 HB, respectively. The severe hardness decreases at 300 °C is attributed to the combined effect of α-Al phase softening and coarsening of the strengthening precipitates. After 200 °C exposure and room-temperature testing, hardness values are equal to the unexposed material, while after 300 °C exposure and room-temperature testing the average hardness reduces to ~80 HB due to the evolution of reinforcing needle-like phase (presumably β'' or β' phase) toward coarser platelet-like θ' precipitates. Finally, as the hardness measurements at high- and room-temperature show almost constant values for each exposure condition, exposing the specimens at 200 °C and 300 °C for 1 h makes the effect of ageing treatment vanish for ageing times longer than 1 h.
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