Andrea Panvini

ABSTRACT The age hardening behavior of gravity cast B356 aluminum alloy was investigated by differential scanning calorimetry (DSC), hardness measurements and tensile tests. Three different artificial aging temperatures were selected, namely 155, 165 and 180 °C, with heat treatment time from 40 min to 32 h. DSC analysis results show that cluster formation begins below room temperature (at around −10 °C). Since cluster formation influences the subsequent precipitation of the main strengthening β'' phase, it can be inferred that a delay between solutionizing and artificial aging has a detrimental effect on the mechanical properties of the alloy. It was also confirmed that the hardness and the tensile properties of the alloy reach the maximum values when β'' phase is completely developed during the artificial aging. This happens after 16 h for samples aged at 155 °C, after 6 h for samples aged at 165 °C and after 4 h for samples aged at 180 °C. A subsequent decrease of the mechanical properties, observed only in the sample aged at the highest temperature, with increasing aging time can be associated with the transformation of the coherent β'' phase into the semi-coherent β' phase. Finally, the activation energy associated with the precipitation of β'' phase was calculated to be 57.2 kJ/mol.

The need to optimise the chemical composition of a diecasting alloy as a function of the technological properties requested by the casting process, led to the development of test apparatus and procedures that allow a comparative assessment of the castability performances in a steel tool and the chemical interaction between the liquid alloy and the die steel. Tests were carried out on a number of copper base alloy, some of which have been modified in order to optimise the technological properties requested by the end product, taking also into account that the alloy is intended to be cast by cold chamber diecasting machine in a hot work steel die. To evaluate the casting behaviour of the alloy in a high thermal conductivity die, a vacuum suction test in a small diameter steel pipe was designed and set up. The measure of the suction length through the pipe due to the pressure difference, allowed a comparison of the fluidity between the tested alloys, at different overheating casting temperatures, and traditional diecasting copper alloy of known performances, taken as the reference alloy. Test results, in terms of suction length and solidified flow front shape, led to the adjustment of chemical composition of a new alloy with better casting performances, overcoming the traditional alloy’s ones. Some static tests were also carried out in order to evaluate the interaction between the liquid alloy and the die steel at high temperature and the effect of alloy iron content and lubricant film on die steel/copper alloy soldering

Uno dei requisiti più importanti delle lamiere di acciaio e delle parti automobilistiche esposte agli agenti atmosferici è la resistenza alla corrosione, che attualmente viene migliorata mediante zincatura. Per gli acciai innovativi di recente impiego, quali gli acciai DP, TRIP TWIP e Q&P non è ancora stato sviluppato un ciclo di trattamento di protezione adeguato e mancano studi sistematici sulle loro proprietà generali di resistenza alla corrosione, per quanto alcuni dati di letteratura mostrino come sia bassa la resistenza alla corrosione degli acciai TWIP in ambienti contenenti cloruri e acido solforico [1-3] e come, similmente, la velocità di corrosione degli acciai TRIP venga accelerata in presenza di elevate concentrazioni di ioni cloruro in soluzione [4]. Considerando che durante il trasporto e lo stoccaggio le lamiere di acciaio possono essere soggette a diverse forme di corrosione ambientale, che possono rendere più difficoltosa la successiva applicazione del rivestimento protettivo, è stato condotto uno studio al fine di valutare la resistenza alla corrosione degli acciai DP1000, TWIP e Q&P, posti in soluzioni acquose caratterizzate da differente aggressività: 0.1M Na2B4O7•10H2O, 0.1M NaCl, 5% HCl e 0.5M H2SO4. Le prove di corrosione sono state effettuate su campioni sia nudi, sia ricoperti dall’ossido di laminazione mediante prove di polarizzazione elettrochimica secondo la norma ASTM G3. I risultati delle prove di corrosione sono stati interpretati sulla base della composizione e della microstruttura degli acciai, che è stata caratterizzata mediante analisi al microscopio ottico e al microscopio elettronico a scansione, dotato di microsonda EDS

Aim of this work is to investigate the effect of adhesive bonding and painting operations performed on B356 T6 aluminum alloy castings. Some parts were produced by gravity casting in steel permanent mold, and were thus treated using three different aging time-temperature combinations according to industrial practice. The castings were then submitted to some thermal cycles to simulate the finishing stages of the production (bonding and painting): such operations are usually performed at temperatures which, in some steps, are close or above to those used duringthe aging heat treatment and may therefore somehow modify the properties of the castings. In order to validate thishypothesis, the mechanical properties before and after the finishing steps were evaluated both on specimens machined from the castings and on separately cast tensile samples. Time and temperature test parameters were selected through the analysis of the industrial cycle. The results of the experimental tests are sho...

ABSTRACT The age hardening behavior of gravity cast B356 aluminum alloy was investigated by differential scanning calorimetry (DSC), hardness measurements and tensile tests. Three different artificial aging temperatures were selected, namely 155, 165 and 180 °C, with heat treatment time from 40 min to 32 h. DSC analysis results show that cluster formation begins below room temperature (at around −10 °C). Since cluster formation influences the subsequent precipitation of the main strengthening β'' phase, it can be inferred that a delay between solutionizing and artificial aging has a detrimental effect on the mechanical properties of the alloy. It was also confirmed that the hardness and the tensile properties of the alloy reach the maximum values when β'' phase is completely developed during the artificial aging. This happens after 16 h for samples aged at 155 °C, after 6 h for samples aged at 165 °C and after 4 h for samples aged at 180 °C. A subsequent decrease of the mechanical properties, observed only in the sample aged at the highest temperature, with increasing aging time can be associated with the transformation of the coherent β'' phase into the semi-coherent β' phase. Finally, the activation energy associated with the precipitation of β'' phase was calculated to be 57.2 kJ/mol.

A review study is presented on microstructural and mechanical properties of Aluminum and Magnesium die-casting parts. Particular emphasis was given to the effects of typical die-casting defects (shrinkage porosity and gas porosity), the possibility of prediction by numerical process simulation and the relation to the resulting die-cast properties. The data available clearly show that a large improvement on overall casting properties is achievable by reducing the defect content on the microstructure either by a more strict control of conventional processes or by the adoption of innovative techniques such as vacuum assisted high pressure die-casting

Weight reduction and material substitution are increasing trends in the automotive industry. High pressure die casting (HPDC) is the conventional casting technology for the high volume production of light alloys; it has recently found wide application in the manufacturing of critical components, such as complex and thin geometry automotive parts. However, the major restriction of this affordable technology is the difficulty to design and realize hollow sections or components with undercuts. An innovative way to further increase the competitiveness of HPDC is to form complex undercut shaped parts through the use of new lost cores that are able endure the high pressures used in HPDC. This paper investigates the use of innovative ceramic lost cores in the production of a passenger car aluminum crossbeam by HPDC. Firstly, process and structural simulations were performed to improve the crossbeam design and check the technology features. The results led to the selection of the process pa...