Solutionizing Effects on Deformation-Induced Phase Transformations in 2014 Aluminum Composite S.K. VARMA, ERICA CORRAL, ERIKA ESQUIVEL, and DANIEL SALAS A solutionizing heat treatment of 2014 aluminum alloy reinforced with 0.15 volume fraction of alumina particles (VFAP) results in deformation-induced precipitation during rolling and tensile deformation, with 0.10 VFAP, at room temperature. The extent of precipitation increases with increase in time and/or temperature of solutionizing. An attempt has been made to identify the various types of precipitates in the samples deformed to a given strain and in fractured conditions. The work- hardening curves and tensile properties of the composites have been shown to be dependent on the time and temperature combination of the solutionizing process. I. INTRODUCTION Monolith of 2014 aluminum alloys indicates the phase transformations during aging, which involve the formation IT has been shown that the microstructures evolved dur- of several kinds of precipitates, including the usual sequence ing the aging process and the age-hardening curves depend of GP zones. [8] The presence of  phase with a stoichiometry on the solutionizing time and temperature in 6061 and 2014 of CuAl 2 , which has a tetragonal structure, is well known, aluminum alloys reinforced with various volume fractions along with its metastable forms  and '. Another phase in of alumina particles (VFAP). [1–6] The composites show the which four metals are present has a chemical formula given formation of a series of Guinier-Preston (GP) zones leading by Al 5 Cu 2 Mg 8 Si 5 , which has a hexagonal crystal structure to the formation of metastable phases ' and ' in 6061 and and has been assigned a symbol of . This  phase also has 2014 aluminum alloy composites, respectively, as a function its metastable counterpart known as ' .The third type of of aging time in a range of temperatures from 160 °C to phase in this system is called the S phase, which has the 220 °C besides another phase ' in 2014 aluminum alloy chemical composition given by Al 2 CuMg with an ortho- composite usually nucleated at the dislocation lines. [1–12] rhombic crystal structure. The effect of increasing solutionizing time at a given temper- Thus, the purpose of this article is to report the results of ature on the age-hardening curves has been found to be such an experimental study to investigate the effect of solutioniz- that the time required to achieve the peak hardness value ing time and/or temperature on the work-hardening charac- decreases in the monoliths, while either a (1) decrease and teristics and microstructural developments in 2014 then increase or (2) decrease and then stabilized values have aluminum alloy and its composites reinforced with 0.1 and been observed for the composites. The generation of disloca- 0.15 VFAP during room-temperature rolling and tensile tions due to the differences in the coefficient of thermal testing. expansion (CTE) values between matrices and reinforce- ments and the concentration of quenched-in vacancies can account for the observed aging behavior of composites and their monoliths. [1–6] The quenched-in vacancies and CTE II. EXPERIMENTAL DETAILS dislocations have been observed to be the nucleation sites for the precipitates originating from the GP zone series (for The composites of 2014 aluminum alloy reinforced with both composites), while CTE dislocations promote the ' 0.1 and 0.15 VFAP were purchased from Duralcan Inc. in precipitation (for 2014 aluminum alloy composite only) dur- rod and sheet forms, respectively. A nominal composition ing aging. of this alloy includes 4.5 pct Cu, 0.88 pct Si, 0.78 pct Mn, An accelerated aging response from the composites con- 0.43 pct Mg, and 0.45 pct Fe, with the balance being taining age hardenable matrix has been well docu- aluminum. The sheets were used for the rolling experi- mented. [11] However, Suresh and Chawla [12] have shown ments, while rods with a gage length of 50.8 mm were that the aging response from a 6061 aluminum alloy in tensile tested with various heat-treated conditions. Three monolith form after a 0.36 pct cold work is similar to the solutionizing temperatures of 520 °C, 540 °C, and 550 °C composite containing 10 pct SiC particles in the unstrained were used in this study in a range of time intervals from condition. This clearly suggests that the dislocations play a 1 to 20 hours. The samples were solutionized in air using very important role in the nucleation of precipitates during a conventional box furnace. All samples were quenched aging treatments. in ice water after solutionizing treatment and were always stored in a refrigerator. Tensile testing was performed on samples with 50.8-mm gage length and 12.5-mm diameter in a Tinius–Olsen tensile testing machine with a crosshead S.K. VARMA, Professor, and ERICA CORRAL, ERIKA ESQUIVEL, speed of 4.2  10 -3 mm/s. The details of rolling and and DANIEL SALAS, Students, are with the Department of Metallurgical sample preparation for transmission electron microscopy and Materials Engineering, The University of Texas at El Paso, El Paso, (TEM) and optical microscopy have been described TX 79968-0520. Manuscript submitted July 27, 1998. elsewhere. [5] METALLURGICAL AND MATERIALS TRANSACTIONS A VOLUME 30A, SEPTEMBER 1999—2539