Improvement of Mechanical Properties of AL Rods

The results of mechanical property tests showed that the method of solution heat treatment and quenching of rods has a significant influence on mechanical properties, which was also related to one of the hypotheses of the diploma thesis. The mechanical properties of tensile strength Rm (N mm-2) after solution heat treatment and quenching on a press are approximately 20 N mm-2 higher than with solution heat treatment in a salt bath and water quenching. ** Similarly, the mechanical properties of yield strength R**p0.2 (N mm-2) are higher after solution heat treatment and quenching of rods on a press, namely by approximately 10 N mm-2.

Problem

The results of mechanical property tests showed that the method of solution heat treatment and quenching of rods has a significant influence on mechanical properties, which was also related to one of the hypotheses of the diploma thesis. The mechanical properties of tensile strength Rm (N mm-2) after solution heat treatment and quenching on a press are approximately 20 N mm-2 higher than with solution heat treatment in a salt bath and water quenching. ** Similarly, the mechanical properties of yield strength R**p0.2 (N mm-2) are higher after solution heat treatment and quenching of rods on a press, namely by approximately

30 N mm-2. The mechanical properties of elongation A4 (%) and hardness HB are higher after solution heat treatment in a salt bath and water quenching. Elongation is higher by approximately

12%, whilst hardness values are higher by approximately 15 HB. Hypothesis H3: Solution heat treatment and quenching on a press improves mechanical properties.

Solution and Method

Hypothesis 3 is partially confirmed, because the hardness value is higher in mechanical properties where solution heat treatment is carried out in a salt bath and water quenching. Elongation is also higher, but this is a consequence of the greater difference between yield strength and tensile strength. Tensile strength and yield strength confirm the stated hypothesis. Tensile straightening by 1–3% also has a significant influence on mechanical properties. ** The mechanical properties of tensile strength Rm (N mm-2) increase after tensile straightening by approximately** 30 N mm-2 with solution heat treatment on a press and water quenching, whilst with solution heat treatment via salt bath and water quenching they increase by approximately

3 N mm-2. Similarly, the mechanical properties of yield strength Rp0.2 (N mm-2) also increased in both cases, namely after tensile straightening where solution heat treatment and water quenching were carried out on a press by approximately 140 N mm-2, whilst with solution heat treatment in a salt bath and water quenching they increased by approximately 110 N mm-2. ** Similarly, hardness HB also increased in both cases,** whilst elongation after tensile straightening is lower in both cases by 3–5%.

The influence of cold deformation by the drawing process, where solution heat treatment and water quenching were carried out on a press, had the greatest influence on mechanical properties on yield strength Rp0.2 (N mm-2). This increased after the drawing process by approximately 140 N mm-2.

Tensile strength Rm (N mm-2) also increased, namely by approximately 30 N mm-2, and hardness HB by approximately 35 HB.

Meanwhile, elongation after cold deformation by the drawing process decreased by approximately

Results

5%. In the case where solution heat treatment was in a salt bath and water quenching, the results were similar, the increase in tensile strength Rm (N mm-2) was slightly smaller, but the value nevertheless increased, namely by approximately 10 N mm-2. Yield strength Rp0.2 (N mm-2) also increased, but also slightly less than with solution heat treatment and water quenching on a press, namely the mechanical properties increased by approximately

110 N mm-2. **Hardness also increased here, namely by approximately 30 HB, whilst elongation A4 decreased by approximately

5%.** H2: Drawing of rods improves machinability and hardness. Hypothesis 2 is fully confirmed, the rods showed improved machinability (narrower tolerance range, better straightness) and increased hardness between 30 HB and 35 HB. The influence of artificial aging on mechanical properties differed according to the time and temperature of artificial aging.

According to the technological path of solution heat treatment and water quenching on a press, the results showed the following findings. Yield strength Rp0.2 (N mm-2) after artificial aging 150 °C/16 h was lower by approximately 10 N mm-2 compared to the technological path without artificial aging.

Meanwhile, the mechanical properties Rp0.2 (N mm-2) after artificial aging 190 °C/8 h were higher by approximately 10 N mm-2. Tensile strengths Rm (N mm-2) after artificial aging 150 °C/16 h and 190 °C/8 h were in both cases worse by 5–10 N mm-2 compared to the technological path without artificial aging.

Elongation A4 in the case of artificial aging 150 °C/16 h was lower by approximately 1%, whilst with artificial aging 190 °C/8 h it was higher by approximately 1% compared to the technological path without artificial aging.

Hardness in both cases of artificial aging decreased by approximately 10 N mm-2 compared to natural aging. Regarding the influence of artificial aging according to the technological path of solution heat treatment via salt bath and water quenching, the results showed the following findings.

Yield strength Rp0.2 (N mm-2) after artificial aging 150 °C/16 h increased by approximately 10 N mm-2, whilst after artificial aging 190 °C/8 h it increased by as much as 85 N mm-2 compared to the same technological path without artificial aging. Tensile strengths Rm (N mm-2) after artificial aging 150 °C/16 h were lower by 20 N mm-2, whilst after artificial aging 190 °C/8 h they were better by approximately 10 N mm-2.

Elongation A4 in the case of artificial aging 150 °C/16 h was very similar, whilst with artificial aging 190 °C/8 h it was lower by approximately 8% compared to the technological path without artificial aging. Hardness in the case of 150 °C/16 h decreased by approximately

15%, whilst after artificial aging 190 °C/8 h it increased by approximately 5%. H1: Artificial aging improves the mechanical properties of aluminium rods.

Hypothesis 1 is partially confirmed. The best mechanical properties were shown by artificial aging 190 °C/8 h, in the case of solution heat treatment in a salt bath and water quenching. An increase in mechanical properties was observed in yield strength, tensile strength and hardness.

However, the hypothesis is not fully confirmed, because elongation after artificial aging is lower by 8% compared to the technological path without artificial aging. The objectives set in the diploma thesis were fully achieved. After each technological path, mechanical properties were determined and the influence of different technological paths on mechanical properties was compared.

It was determined which technological operations represent an improvement in mechanical properties and which do not increase them. By presenting the entire process, which begins with the preparation of a work order, preparation of raw material, pressing and other technological operations, they presented how the final product – the rod – is obtained. [deof_form download_text="Sergej-Godec_dd.docx" download_url="https://www.academia.si/novice/wp-content/uploads/2018/09/Sergej-Godec_dd.docx"]