M. Nageswara Rao

Use of Strain Energy Density W and Qo as Quality Indices for Rating the Quality of Cast Aluminium Alloy354 as a Function of Processing Parameters

Cast aluminium alloy 354 has found widespread application in the automotive industry for its excellent mechanical properties and good castability. The stringent emission norms and demands for improved fuel economy have pushed automobile technology to new frontiers. This has led to efforts to reduce weight while maintaining higher vehicle performance. Cast aluminium alloy 354 is a material that performs with reasonable effectiveness in the high stress automobile environment. The present study looks at the use of strain energy density W and the quality index Qo to determine the effect of process parameters like aging temperature and modification on the quality of the alloy 354 and also to monitor the effect of interrupted heat treatments T6I4 and T6I6 on the quality of the material. The strain energy density W calculated for the interrupted heat treatments on alloy 354 show a broad inverse relation with yield strength Rp. An improvement in the yield strength and the strain energy density of the alloy is observed when the alloy is subjected to modification. At artificial aging temperatures lower than the artificial aging temperature adopted in standard aging treatment an improvement in the Qo and W quality of the alloy 354 have been observed.

Weibull Analysis of the Effect of Modified Aging Treatments on Fatigue Life of Cast Aluminium Alloy 354

Cast aluminium alloy 354 has extensive applications in the automobile industry. Due to its attractive combination of mechanical properties and excellent castability, it is being used in production of automobile components like the compressor wheel for turbochargers. Performance of this component under fatigue loading conditions is a critical issue. The present study explores the possibility of improving the fatigue life of the component by bringing in process changes (i) adopting a two-step aging treatment in place of the normally used single step aging treatment (ii) adopting a lower artificial aging temperature (171°C) instead of the temperature normally used for artificial aging (188°C) while performing T61 treatment. In all cases Weibull analysis of fatigue test results was carried out. Weibull analysis of Ultimate Tensile Strength (UTS) values obtained after artificial aging at 171°C and 188°C was also carried out. Among the four variants of two-step aging treatment carried out, the one consisting of 100°C for 5 hours followed by 170°C for 5 hours was found to have the best characteristic fatigue life for the components. The modified T61 treatment where aging was carried out at 171°C instead of the normally used 188°C yielded better characteristic fatigue life as well as better Ultimate Tensile Strength (UTS).

Effect of Modified Aging Treatments on the Tensile Properties, Quality Indices and Fatigue Life of Cast Components of Aluminum Alloy 354

With the drive to build higher performance automobile engines, there has been a steady demand to further improve the mechanical behavior of the cast aluminum alloy 354 through improvements in processing. The present study explores the possibility of improving the tensile properties, quality indices Q & QC and fatigue life of the alloy over those obtained by standard T61 treatment by adopting different modified aging treatments. These include i) lowering the artificial aging temperature ii) interrupted aging cycles similar to T6I4 referred to in the published literature and iii) artificial aging in two steps instead of in single step. Based on the results, a few modified aging treatments could be identified which lead to a comparable combination of tensile properties, but with improved fatigue life and a shade higher quality level.

Effect of Non-Conventional Aging Treatments on the Tensile Properties of Non-Hipped Castings of Aluminum Alloy 354

Cast aluminum alloy 354 is used extensively for production of critical automobile components, owing to its excellent castability and attractive combination of mechanical properties after heat-treatment. With the advent of higher performance engines, there has been a steady demand to further improve the mechanical behavior of the castings made of the alloy, among others, through improvements in processing. The present study explores the possibility of improving tensile properties of the alloy by adopting certain non-conventional aging treatments. The non-conventional treatments include aging cycles similar to T6I4 and T6I6 referred to in the published literature, artificial aging in two steps instead of in single step and artificial aging preceded by various natural aging times. The results show that none of these non-conventional treatments leads to improvement of all tensile properties compared to the standard T61 treatment. Significant hardening takes place in the alloy due to natural aging. Changing the time of natural aging preceding artificial aging was found to have little effect on tensile properties.

Effect of Non-Conventional Aging Treatments on the Tensile Properties and Quality Indices of Hipped Components Made of Cast Aluminum Alloy 354

Cast aluminum alloy 354 is used extensively for production of critical automobile component, owing to its excellent castability and attractive combination of mechanical properties. With the advent of higher performance engines, there has been a steady demand to further improve the mechanical behavior of the alloy, among others, through improvements in processing. The present study explores the possibility of improving mechanical behavior and quality levels of the alloy by adopting certain non-conventional aging treatments. Quality indices Q and QC have been used for quality rating. The non-conventional treatments include aging cycles similar to T6I4 and T6I6 referred to in the published literature, artificial aging in two steps instead of in single step and artificial aging preceded by various natural aging times. The results show that none of the non-conventional treatments leads to improvement of all tensile properties compared to the standard T61 treatment. However, some specific treatments could be identified which lead to a comparable combination of tensile properties and a shade higher quality level. Increasing the time of preceding natural aging does not help in improving the tensile properties after artificial aging.

Strain Hardening Behaviour of Hipped and Non-Hipped Castings of Aluminium Alloy 354 Subjected to Two-Step Ageing Treatments

Cast aluminium alloys are being employed increasingly in the automotive sector due to their light weight and excellent castability. This paper focuses on the strain hardening behaviour of Hipped and non-Hipped components of cast aluminium alloy 354 subjected to two-step ageing, as opposed to the routinely carried out single-step ageing. First step ageing (at 100°C) was carried out for 2 h and 5 h; ageing time at second step (at 170°C) was 1, 2 and 5 h. Mechanical properties and strain hardening behaviour were evaluated for different variants of two-step ageing treatment. Analysis of the results shows that the Hipped components have higher hardening capacity and generally higher strain hardening rate compared to the non-Hipped ones. Some of the two-step ageing treatments give mechanical properties comparable to the conventional T61 treatment, but with significantly higher strain hardening rate.

Effect of Various Non Conventional Aging Treatments on the Mechanical Properties and Quality Indices of Cast and Heat Treated Components of Aluminum Alloy 354

Cast aluminum alloy 354 is widely used for production of critical automobile components, thanks to its outstanding castability and attractive combination of mechanical properties in heat-treated condition. With the engines of higher performance entering the scene, there has been a constant demand to further improve the mechanical behavior of the castings made of the alloy. Exploring improvements in processing has been one important approach in this context. The present study explores the possibility of improving tensile properties of the alloy by adopting certain non-conventional aging treatments. The treatments include aging cycles similar to T6I4 and T6I6 referred to in the published literature, artificial aging in two steps instead of in single step and artificial aging preceded by various natural aging times. The results show that these nonconventional treatments do not lead to overall improvement of tensile properties compared to the standard T61 treatment.

Weibull Analysis of the Effect of Interrupted Aging Treatments on the Fatigue Life of Components Made of Cast Aluminium Alloy 354

Cast aluminum alloy 354 is widely used in the automobile industry due to its attractive set of mechanical properties and excellent castability. The compressor wheel in turbochargers, for example, is used for the production of this alloy. Apart from mechanical properties like fracture toughness and tensile strength, the fatigue life of the component is also a critical issue while considering the performance. This study makes an attempt to improve the fatigue life of a component made out of this alloy by subjecting it to interrupted aging cycles similar to T6I4 and T6I6 (discussed in the published literature) instead of the normally used T61 standard aging treatment. Results show that subjecting the material to these interrupted aging treatments gives lower fatigue life than that obtained after subjecting it to standard T61 conditions.Also, T6I4 treatment yields better fatigue life as compared to T6I6.

Analysis of Strain Hardening Behaviour of Cast Aluminium Alloy 354 Subjected to Artificial Ageing at Various Temperatures

Automotive industry makes wide scale use of cast aluminium alloy 354 in the production of crucial components, such as compressor wheels for turbochargers. The compressor wheels undergo T61 heat treatment, involving artificial ageing at 188°C. This study focuses on the possible improvement of the mechanical behaviour of the components by subjecting them to modified heat treatments involving usage of lower artificial ageing temperatures (160, 171 and 177°C). A comparative analysis of tensile properties and strain hardening behaviour has been carried out with different artificial ageing temperatures. Results showed that the heat treatment routinely employed by the industry (aged at 188°C) leads to overageing, thereby resulting in relatively inferior mechanical properties and lower strain hardening rates as compared to the samples heat treated at lower artificial ageing temperatures. It is concluded that lowering of the artificial ageing temperature can lead to a superior state of components with respect to mechanical behaviour.