Phase formation in as-solidified and heat-treated Al–Si–Cu–Mg–Ni alloys: Thermodynamic assessment and experimental investigation for alloy design

The effects of cooling rate and heat treatment on mechanical and thermal characteristics of Al–Si–Cu–Mg foundry alloys

Effect of Fe content on the fracture behaviour of Al–Si–Cu cast alloys

HRTEM and HAADF-STEM of precipitates at peak ageing of cast A319 aluminium alloy

The aim of the present work is the study of T6 heat treatment of A354 (Al-Si-Cu-Mg) casting alloy. The heat treatment was optimized by maximizing mechanical strength of the alloy while keeping the treatment cost effective, reducing treatment time and temperature. Due to the presence of low melting compounds, a double stage solution treatment was proposed. The first stage was aimed at the homogenization and dissolution of the low melting phase while a second stage at a higher temperature was evaluated to foster dissolution of Cu/Mg rich intermetallics and keep the solution time and temperature as low as possible. Microstructural investigations were performed through optical and electronic microscopy, which allowed the assessment of the evolution of intermetallic phases during the solution treatment. Artificial aging was studied at different temperatures from 160 °C to 210 °C where the peak aging condition was identified. Over aging of the heat treated alloy was evaluated by soaking T6 samples at 200, 245, and 290 °C for up to 168 h. Tensile behavior of the T6 and over-aged alloy (i.e., after soaking at 210 °C for 50 h) was evaluated at room temperature. Results showed that the proposed treatment allowed the enhancement of mechanical properties of the alloy in comparison to industrial practice treatment, maintaining a good level of ductility and conferring a superior resistance to long-term high temperature exposure.

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Optimization of A354 Al-Si-Cu-Mg Alloy Heat Treatment: Effect on Microstructure, Hardness, and Tensile Properties of Peak Aged and Overaged Alloy

The current study was carried out with a view to investigating the influence of age-hardening parameters, aging temperature and time, on the tensile properties and quality indices of a high-strength Al-9 pct Si casting alloy, namely, 354-Al-9 pct Si-1.8 pct Cu-0.5 pct Mg. Quality charts were used as an evaluation tool for selecting the optimum conditions to be applied, in practice, in order to develop high strength and optimum quality in 354 casting alloy. Aging at a low temperature of 428 K (155 °C) was observed to produce the greatest strength and optimum quality in the 354-type castings compared to aging at higher temperatures. The peak strength observed for 354 alloy may be attained after shorter aging times on the condition that the aging temperature is increased. The aging times required for reaching peak strength in 354 alloys are 72 hours, 40 hours, 8 hours, 1 hour, and 15 minutes at aging temperatures of 428 K, 443 K, 468 K, 493 K, and 518 K (155 °C, 170 °C, 195 °C, 220 °C, and 245 °C), respectively. Aging treatment at higher temperatures is accompanied by a reduction in the tensile properties and quality index values of the castings; however, it also introduces the possibility of a significant economical strategy for minimizing the time and the cost of this same treatment. Aging treatment at a lower temperature of 428 K (155 °C) produces fine and dense precipitates displaying smaller interparticle spacing, while at higher aging temperatures, such as 518 K (245 °C), the precipitates are coarser in size, less dense, and more widely dispersed. The quality charts developed in the course of the current research facilitate the interpretation and evaluation of the tensile properties of the 354 alloy. Such charts provide a logical evaluation tool, from the metallurgical point of view, for an accurate prediction of the influence of aging parameters studied on the properties of the alloys. Depending on the required level of tensile properties and based on the quality charts developed, it is possible to make a rigorous selection as to the most suitable aging parameters to be applied to the 354 alloy so as to obtain the best possible cost-effective compromise between alloy strength and quality.

Influence of Aging Parameters on the Tensile Properties and Quality Index of Al-9 Pct Si-1.8 Pct Cu-0.5 Pct Mg 354-Type Casting Alloys

In the current study, the influence of solution heat treatment and aging conditions on the strength and quality index of 354 castings was investigated. Increasing the solutionizing temperature up to 525 °C increased the strength and quality index values of 354 castings containing different levels of iron. A prolonged solutionizing time was also found to further improve the alloy mechanical properties and quality index. The addition of strontium to the 354 alloys noticeably affected the response of these castings to solution heat treatment through reducing the solutionizing time required to achieve the same level of properties as the non-modified castings. Aging treatment provided a wide range of mechanical properties and quality index values according to the aging conditions (temperatures/times) employed. Aging at 245 °C provides significant economical benefits as peak aging occurs after only 15 min of aging. However, this is accompanied by a slight reduction in tensile properties and quality index value of the alloy as compared to aging at a lower temperature of 155 °C.

G. K. Sigworth

Papers

Influence of Aging Parameters on the Tensile Properties and Quality Index of Al-9 Pct Si-1.8 Pct Cu-0.5 Pct Mg 354-Type Casting Alloys

Appropriate Heat Treatment Procedures for Improving Strength and Quality Index in 354 Casting Alloys